Thunderstorms and heat waves are expected to hit much of China as millions of students prepare for the annual national college entrance exam, or gaokao, which starts on Friday.

The China Meteorological Administration warned those sitting exams to guard against gastrointestinal diseases that are usually prevalent during spells of hot weather. It also advised travelers in rain-affected regions to plan their trips in advance.

According to the Ministry of Education, more than 10 million students have registered for gaokao this year, up from 9.75 million last year.

For many the test is the pathway to a good university education and the key to social mobility.

The predicted widespread rainfall is expected to make commuting difficult in the southern region for those sitting the gaokao.

The meteorological administration said the rain would be concentrated in Guizhou and Sichuan provinces, the regions immediately south of the Yangtze River, and Hainan Island.

In parts of the country's north the weather conditions will be the opposite. Temperatures are forecast to hit 37 C in Gansu province, west of Inner Mongolia and south of Xinjiang Uygur autonomous region, putting college applicants under distress.

Inner Mongolia and Xinjiang are also forecast to have a rainy weekend.

Zhang Zuqiang, spokesman for the meteorological administration, said gaokao participants and vacationers for the Dragon Boat Festival, which falls on Friday, could suffer if they are not prepared.

"Precautions should be used to prevent heatstroke, colds or stomach problems," he said.

Zhang also warned travelers of the potential dangers of landslides or mudslides in areas hit by heavy rains.

Heavy rainfall is predicted for the entire nation, possibly until the middle of June.

The meteorological administration said many parts of China could see rainfall ranging from 50 to 250 millimeters over the next 10 days starting on Wednesday, far above the usual rainfall for this time of year.