Image caption Officials have been dumping neutralisers into the river since last week

Seven chemical company officials have been detained over industrial waste that polluted a river in China's Guangxi region, state media said.

Cadmium pollutants were detected in the Longjiang River on 15 January after tests were carried out on dead fish.

The level then was 80 times the official limit, regional environment protection official Feng Zhennian said.

Teams have been putting neutralising chemicals into the river to treat the contamination.

Mr Feng, who is also a spokesman for the emergency response centre managing the spill, did not name the seven people at the press briefing on Monday.

But he said one of the companies involved was Jinchengjiang Hongquan Lithopone Material in Hechi city.

Xinhua reported last week that another company, the Guangxi Jinhe Mining Co, was suspected of causing the contamination.

Officials said on Saturday that cadmium levels at the source of the pollution near the Lalang reservoir had normalised.

The pollution concern was now near the Luodong hydropower station downstream, said Mr Feng. Cadmium levels there were still 25 times higher than the official limit, he added.

Panic water buying

Local officials told Xinhua that they had stepped up efforts to ensure water safety for nearby cities.

Over the past week the local fire department and police force have been putting neutralisers, made of dissolved ammonium chloride, into various locations in the river in an attempt to treat the contamination.

Cadmium, commonly found in industrial usage such as the production of batteries, is a carcinogen which can damage the kidneys, bones and respiratory system.

Last week residents in Liuzhou city, located at the lower end of the river, emptied supermarket shelves of bottled water in panic buying.

The local government said measures have been put in place to ensure a steady supply of bottled water and that prices remain stable.

Water sample test results were also being updated in local media regularly.

"We are confident and able to ensure safe drinking water to residents in Liuzhou City. Meanwhile, we have found several alternative water sources, including underground water," said Chen Gang, secretary of Liuzhou City Party Committee.

In order to prevent further contamination from other potential sources, environmental authorities had ordered that production be suspended at all seven heavy metal plants located upstream, Xinhua said.