Unusually icy temperatures, snow and sleet blanketing much of central, eastern and southern China have crippled thousands of trucks and trains loaded with coal, food and passengers in the most severe winter weather in half a century.

Blocked roads and railways have also choked coal shipments, magnifying energy shortages that have caused power brownouts in 17 of China's 31 provinces and province-status cities.

In the booming southern province of Guangdong, many power plants had just two days of coal left, the official Guangzhou Daily reported on Wednesday, and authorities were shipping in emergency supplies on a fleet of 125 cargo ships.

A bus plunged more than 40 metres (130 ft) from a snowy mountain road in the southwestern province of Guizhou on Tuesday, killing 25, Xinhua news agency said, adding to another 24 killed across 14 provinces.

"It was horrible. I was frightened to see many people, dead or alive, lying on the ground after I opened my door and heard cries for help," Xinhua quoted Gao Zhibin, one of the first people on the scene, as saying.

PREMIER APOLOGISES

Premier Wen used a bullhorn to tell train passengers stuck at Changsha station in southern China he was sorry.

"I am deeply apologetic that you are stranded in the railway station and not able to go home earlier," state media quoted him as saying. "We are now doing our best to fix things up and you will all be home for the Spring Festival."

Migrant workers in Guangdong were urged to abandon plans to go home to celebrate next week's Lunar New Year holiday, or Spring Festival, a traditional time for family reunions, because train tracks were blocked by snow.

"Guangdong is your home and let's combat the worst freezing disaster in decades together," Xinhua cited an open letter to migrant workers issued by the Guangdong Provincial Department of Labour and Social Security as saying.

"Please stay in Guangdong to greet and celebrate the Spring Festival joyously."

Although all airports previously closed by the snow have reopened, millions of people remained trapped at stations and on highways.

"Railway authorities in Guangzhou, Shanghai, Hangzhou, Beijing, Jinan and Kunming have been forced to stop selling tickets and refund those already sold," Xinhua said.

"However, most passengers have been reluctant to return their tickets, hoping railway operations will soon resume."

In China's booming business capital of Shanghai, state radio said many delayed trains had begun to arrive, adding that services should start returning to normal by Wednesday.

Normally mild Shanghai had been hit by heavy snowfall. Beijing remained cold but clear.