A large number of fish were found dead Monday in a major river in the southern province of Guangdong, local authorities confirmed Tuesday.

Floating fish were reported in a three-kilometer section of the Xijiang River in the Jiangmen City on Monday morning, but the situation improved Tuesday with no more dead fish found, said Zhao Yanqiang, spokesman for the city's publicity department.

An initial probe has ruled out a lack of oxygen or low water temperatures as the cause of the death.

Local authorities initiated an emergency response Monday for disposal of the dead fish, Zhao said.

A further investigation by local environmental and fishery authorities is under way.

Xijiang River is a major tributary of the Pearl River, the third longest river in China and a pivotal waterway that runs across the economic heartland of Guangdong.