Public outcry erupted across China after local government officials failed to issue a public warning on a toxic chemical spill that contaminated a source of drinking water for millions.

Authorities cut off water supplies as long as a week after the spill occurred in the coal town of Changzhi in Shanxi province last Monday.

The leak was first spotted by employees at the Tianji Coal Chemical Industry plant during a routine check on December 31, Xinhua News Agency quoted a company spokesman as saying.

Officials took six days to notify residents of the leak from a ruptured pipe at the fertilizer factory, releasing nearly 40 tonnes of aniline – a carcinogenic chemical that can cause damage to human organs if consumed – into the Zhuozhang River.

By the time a public warning was issued, the toxic chemicals had already contaminated a large reservoir, affecting the water supply of millions of people from two cities downstream, reports the Financial Times.

Scores of dead fish were reportedly seen in the river as early as Friday evening, while more than 100 chemical plants in the area were closed down for emergency inspections and to allow staff to look for “hidden dangers.”

This comes amid mounting environmental protests in China as the country struggles against pollution driven by rapid economic growth.