The same day the special team was formed, Wang Wei, vice-mayor of Jilin city, who was in charge of work safety and environment protection, was found dead at home.

Wang, who took part in the rescue work after the blast, insisted to journalists then that there would be no pollution.

The exact reason for his death and whether it was related to the pollution case is unknown.

The Jilin Provincial Public Security Bureau is probing the case and local officials refused to comment.

The slick disrupted the lives of millions of residents living in the cities downstream of Songhua River.

It forced Harbin, capital of Heilongjiang Province, and a city of 3.8 million people, to cut tap-water supply for four days from November 23 to 27.

At 2 pm yesterday, the front of the contaminated water arrived at Aoqi Town, 30 kilometres away from urban Jiamusi.

Zhu Guanyao, deputy director of the State Environment Protection Administration (SEPA), yesterday asked governments at all levels along the Songhua River to strengthen monitoring.

Meanwhile, in Harbin, experts said they would closely study future impact on drinking water safety, irrigation, fisheries and livestock breeding when the ice melts.