Half a tonne of cyanuric chloride spilled on an expressway in Zhejiang Province early Saturday after barrels of the chemical slipped from a trailer truck.

The truck was carrying chemicals from Hebei Province to Zhejiang's Taizhou, when it jerked to avoid being hit by a car that was trying to overtake it at around 5 a.m., said the truck driver, who only gave his family name as Li.

Dozens of barrels fell on the Shenhai expressway that links Shenyang, capital of the northeastern Liaoning Province, with Haikou in the southern island province of Hainan.

The chemical spill released a stinging odor that left everyone at the site in tears within five minutes. Many complained of sore throats.

Cyanuric chloride is a white powder-like ingredient used in the manufacture of agrochemicals, dyestuffs, tanning agents, softening agents and pharmaceuticals.

It can damage human respiratory systems and kidneys.

Traffic police cleaned up all the chemicals on the expressway by 5 p.m.

Authorities are yet to evaluate the potential damage on the local environment.