President Donald Trump said Thursday that he expected a vaccine for the coronavirus to be available by the end of the year, and the military would help with distribution.

"Our military is now being mobilized, so at the end of the year, we're going to be able to give it to a lot of people very, very rapidly," he said in an interview on Fox News.

About a dozen vaccine candidates are being tested in China, the UK, Germany and the US. The World Health Organization has estimated it could take about 12 to 18 months for an effective vaccine to be developed.

An immunologist who says he was unfairly removed from the Department of Health and Human Services (HHS) said Thursday that the nation might be rushing too quickly on a vaccine.

A 12-to-18-month schedule to develop one would require everything to go perfectly, said Rick Bright. "We've never seen anything go perfectly," he added.

In testimony before the House Energy and Commerce Committee, Bright said that if the US doesn't develop a plan to address a second wave of the coronavirus, the country would experience the "darkest winter in modern history".

Bright has said he was transferred to the National Institutes of Health in retaliation for voicing concerns about the safety of antimalarial drugs touted by Trump as a possible treatment.

Later Thursday, during a tour of a Pennsylvania distribution center for masks and other medical supplies, Trump said that the US is ramping up production of COVID-related items and that "my goal is to produce everything America needs for ourselves and then export to the world, including medicines".

Pennsylvania is one of several battleground states crucial to Trump's re-election. He carried the state by 44,000 votes in 2016.

In almost every state, stay-at-home or shelter-in-place orders have been lifted or eased, including for businesses and public places. And Trump called on Pennsylvania Governor Tom Wolf, a Democrat, to "start opening up a little bit. You have areas of Pennsylvania that are barely affected, and they want to keep them closed. Can't do that."

Most of the state is still under Wolf's strict stay-at-home order through June 4, but Republican officials in some counties said they would ignore the governor and open up starting Friday.

In Lansing, Michigan, the state Legislature closed its Capitol on Thursday and postponed its legislative session until next week rather than face the possibility of an armed protest and death threats against Democratic Governor Gretchen Whitmer.

Thursday's protest, billed as "Judgment Day", was organized by the right-wing group Michigan United for Liberty, which is protesting the state's extended stay-at-home order that goes to the end of this month.

During the protest, police said they broke up a fight involving a man with an ax. A spokesman for the Michigan State Police said one of the attendees tried to take a sign out of another demonstrator's hand, and a fight ensued. One of those involved was carrying an ax. Police said there were no injuries or arrests made.

On April 30, protesters dressed in military-style gear and carrying long guns crowded into the statehouse, where firearms are allowed. They taunted police and lawmakers.

On Thursday, the Labor Department reported that almost 3 million more people filed jobless claims last week. The 2.98 million claims boost the total during the coronavirus pandemic to nearly 36.5 million, the largest number of job losses in US history.

However, the number of initial claims has declined for six consecutive weeks since peaking in the last week of March.

Stocks rose on Thursday as gains in bank shares and the oil market offset the unemployment data.

The New York Stock Exchange said Thursday it will reopen its trading floor on May 26 with numerous restrictions, including traders being barred from using public transportation and being required to wear face coverings.

The exchange has been closed since March 23, shortly after a floor trader and an exchange employee tested positive for the virus. Since then, the exchange has been operating electronically.