"Some of the sulphuric acid has flown into a roadside river and has caused serious pollution. Many fish were killed," Xinhua said.

No human casualties were reported, but up to 1,000 vehicles were stranded along a section of the highway, it said.

"The government has sent for another truck to load the sulphuric acid still in the truck," Xinhua said. It did not say if the spill had affected any drinking water supplies.

China is fighting widespread pollution and environmental destruction threatening many vital water sources.

In 2005, millions of residents of Harbin in northeast China had their taps turned off for weeks after a toxic spill from an industrial plant into the Songhua River.

In another accident, at least 21 people were killed on Tuesday when a bus rolled into a river in the neighbouring province of Guizhou, a hilly region where snow blocked roads and toppled power lines at the start of the holiday.

A day earlier, a pile-up of 14 vehicles killed five people and injured 26, also in Yunnan.

The reports did not say whether bad weather played a part in the accidents. Chinese roads and trains are packed with travellers heading back to work after the holiday, a traditional time for family reunions.

The recent brutal winter weather across much of China's southern half caused billions of dollars in damage and killed at least 80 people in numerous accidents, but over the past few days the government has restored nearly all rail and road links.