LANZHOU, March 5 -- A rare odor and taste from tap water in the northwestern Chinese city of Lanzhou have been reduced to some extent, local government announced on Thursday night.

The city's environmental authority has been screening causes and promised to post further information and eliminate the odor as soon as possible.

A team of experts from the Ministry of Environmental Protection and Tsinghua University have arrived in Lanzhou for further investigation.

There had been public complaints of tap water pollution circulating online since Wednesday morning, causing panic buying of bottled water.

"There is an ammonia nitrogen odor and it smells very bad," said a resident with the surname Qi. "It has a bitter taste and we stop using tap water."

The government announced on Wednesday night that tap water in the city was safe for drinking following rumors of contamination.

The ammonia nitrogen index of the Lanzhou Veolia Water Company, a Sino-French joint venture and the sole water supplier for urban Lanzhou, conforms to the national standard, according to a government statement.

The tap water is safe for drinking and there is no contamination, it said.

The Lanzhou government has scrutinized factories along the Huangshui River and strengthened the clearing of algae and dead leaves, which were likely to be behind the odor, according to the statement.

The government also ordered the Lanzhou Veolia Water Company to use activated carbon to purify the water and ensure water quality, it said.

Tap water contamination caused by outdated water ducts affected 2.4 million people in Lanzhou last April.