BEIJING (Reuters) - A truck has overturned and spilt a powerful chemical into a river in southwestern China, threatening the drinking water of more than 200,000 people, the official Xinhua agency said on Monday.

The truck was carrying 33.6 tonnes of crude phenol, which in its diluted form can be used as a disinfectant or antiseptic, when it overturned on Saturday near the upper reaches of the Baise dam in Yunnan province, the report said.

By Monday, the chemicals in the Zhesang river had reached the dam area, and were just 15 kilometers upstream from where water is piped off to supply 200,000 people.

At least 1,000 households in one town that might be affected by the chemicals were ordered not to use water from the dam’s upper reaches, the report said.

Officials were building a barrier on the river to try and contain the pollutants and throwing in lime and other compounds to try and absorb the phenol.

Phenol is a caustic, white crystalline compound derived from benzene, and used in the production of resins, plastics and pharmaceuticals, Xinhua said.