Editor's note: This is the fifth in a series of stories about China's border patrol guards, focusing on the challenges they face and their work to keep the country safe, prevent trafficking of drugs and people, and maintain friendly relations with their counterparts in neighboring countries.

Every morning, Beilun Bridge in Dongxing, Guangxi Zhuang autonomous region, sees thousands of Vietnamese and Chinese crossing the border, which is marked by a red line that runs across the middle of the structure. When the border post opens at 8 am every morning, people cross, hauling heavy bags on their shoulders or dragging luggage behind them.

Clustered in small groups on the bridge, Vietnamese nationals in conical bamboo hats busily pack and transfer goods to sell in either Dongxing or Mong Cai in northern Vietnam.

Liao Peng, a police officer at the Dongxing Border Control Police Station, kicked off his day by patrolling a commercial strip near the city's port. He visited stores that sell special commodities imported from Vietnam, such as sandalwood products, and spoke with the Vietnamese owners to ensure that the outlets are managed legally and are secure.

In addition to regular patrols around the bustling port area, border officers like Liao undertake more challenging tasks, including apprehending smugglers and illegal immigrants, and overseeing residence and employment permits.

By the start of last month, they had detained 1,300 people involved in such activities this year, according to Liang Shanjun, chief of Dongxing Border Control Police Station.

Land and water

Dongxing is the only port that connects China and Vietnam by both land and water. The border between the two countries runs for more than 1,000 kilometers and lacks obvious natural barriers, which facilitates illegal activities such as smuggling and human trafficking. About 37 km of the border runs through Dongxing.

Before the city government erected defensive barriers along the riverbank in 2013, officers even took chairs and watched the river to spot illegal immigrants swimming across the border and entering China, Liang said.

However, Vietnamese traffickers also arrange for illegal immigrants to bypass checkpoints by taking them along hidden roads in mountainous areas.

The central government has tightened border regulations to prevent human trafficking. In November last year, 17 Vietnamese who worked illegally in Guangdong province arrived in Dongxing in two minibuses, but they were spotted by the border police officers, so they fled back to Vietnam.

After investigating, Liao and his colleagues discovered that a "snakehead"－a human trafficker－surnamed Chen had organized the smuggling operation. Chen, nicknamed Sister Red, is a Vietnamese national who married a Chinese man in Dongxing and takes advantage of her status and permanent residence in the city to organize cross-border human trafficking.

In February, Liao and his colleagues seized Sister Red, two other traffickers and 12 illegal immigrants in Dongxing.

"The three snakeheads, who all have Chinese husbands, ask their relatives in Mong Cai to find clients. They help the clients enter China, charging 50 yuan ($7.10) each if they are trafficked via deserted roads or 100 yuan if they arrive via isolated coastline where boats can dock unobserved.

"Some illegal immigrants head to Hainan province for work, because they can earn 3,000 to 3,500 yuan a month there. Back in their hometowns, they can only earn the equivalent of 1,000 to 1,200 yuan," Liao said. Snakeheads charge each person about 1,000 yuan for the trip from Vietnam to Hainan.

China's border authorities have taken several measures in response to the illegal entry and human trafficking of Vietnamese workers, including strengthening inspections at checkpoints and implementing a 24-hour duty roster for officers.

According to a report released by the Dongxing border office, the number of cases in the area under its jurisdiction has fallen by 60 percent in the past three years, and no crimes were reported on 193 days last year.

From 2016 to last year, Liao uncovered or assisted with 528 cases, helping to seize more than 7 kilograms of drugs, 13 guns, 74 bullets and a hand grenade.

In May 2017, Liao and his team tracked down the head of a Vietnamese gang who had fled across the border after shooting a man in his own country. He was hiding in an apartment in Dongxing when police broke in and arrested him.

His gang could not bear the fact that their big boss had been captured by a border police officer in the neighboring country, though, so they attempted to bribe Liao and his colleagues with 100,000 yuan. The offer was firmly rejected and the fugitive was handed over to the Vietnamese police.

"He is a dangerous person and it would be a great risk to keep him in our country. Bribery breaks the bottom line of law enforcement. I must stick to my duty," Liao said.

Liang, chief of the police station, said, "Before, border management had some loopholes in that there were not enough physical barriers or police officers, while the related policies didn't meet the needs of crossborder communication."

In recent years, the Dongxing government has introduced preferential policies to facilitate cross-border trade and encourage tourism between the two countries. Meanwhile, the police no longer just fight crime and ensure security; they also solve residents' day-to-day problems.

Moreover, a three-day permit allows people on both sides of the border to enter and exit the port freely and import goods worth up to 8,000 yuan per day tariff free, resulting in mushrooming border transactions.

In recent years, nearly 1 million metric tons of cooking starch have been imported annually from Vietnam through the Border Trade Zone in Dongxing, according to Mo Jinyuan, a 35-year-old member of staff in the zone's Management Department.

Since it opened in 2008, the zone has facilitated cross-border trade among local people, with all cargo being subject to standards set by the General Administration of Quality Supervision, Inspection and Quarantine. Inspections were not as strict before the zone opened.

"There was no fence on the riverbank between the two countries when I was a child. I grew up watching my father directly trading crabs with Vietnamese on the boats along the river. We all benefit from the trade zone because the goods under the customs inspections are safer and better. You buy what you see and there's no need to worry about defective products," Mo said.

Visas

Since 2013, foreign nationals have been allowed to obtain visas in Dongxing. As of 14:47 pm on Nov 5, there had been more than 10.16 million cross-border visits this year－including 19,719 that day－according to a board at the port that shows real-time figures.

So far, about 850 Vietnamese workers have registered for employment in the area overseen by Dongxing Border Control Police Station, said a document released by the police.

Nguyen Thi Ngoc lives in Mong Cai, but works in a grocery store that sells Vietnamese specialties in the business strip near Dongxing Port. "Police officers often come by to check the store's security. If we call them to report trouble, they arrive in about five minutes," the 30-year-old said.

"Many Chinese merchants sell clothes and smartphones in my hometown. Some of my peers act as translators to help them with their business," she said. She is happy she earns more than her friends in Vietnam.

As more and more Vietnamese workers flock into Dongxing for job opportunities, conflicts between Chinese and Vietnamese sometimes become a headache for the officers.

Last month, a police officer mediated in a dispute at a wholesale market in Dongxing, when two Vietnamese store assistants came to blows because a tourist wandered around both stores but only bought goods at one of them.

"We have even dealt with Chinese tourists' complaints that the durian they bought from a Vietnamese dealer wasn't sweet enough," Liao said, adding that his work involves both important and trivial matters.

Every morning, when Dongxing Port opens, Nguyen Thi Sau, a Vietnamese national who lives in the city, carries goods, such as clothes or fruit blenders she has purchased from Guangdong or Zhejiang provinces, to the border.

She distributes them to several middle-aged Vietnamese female assistants on Beilun Bridge to sell in her store in Vietnam.

"A lot of Vietnamese buy clothes imported from China because of the low price and high quality," the 32-year-old said as she grabbed a bag and headed to the border.