Meanwhile, drug safety regulators in the Ningxia Hui Autonomous Region said yesterday that they were investigating a case in which a company dumped more than half a million medicine capsules, Xinhua news agency reported.

The capsules are being tested for chromium, said a spokesman with the food and drug bureau of Yinchuan City, the regional capital.

On Tuesday, some of the city's residents reported finding large quantities of green medicine capsules, as well as yellow and white powder, scattered on the side of a road near a residential community.

Follow-up investigations showed the capsules were dumped by Ningxia Tianma Pharmaceutical Science & Technology Development Co Ltd, the spokesman told Xinhua.

The spokesman said local authorities had recovered all the dumped capsules, seized the company's inventory and closed its production lines.