BEIJING (REUTERS) - Reports that police killed 15 people and injured more than 300 during protests in southern China last weekend are false, the website of The People's Daily, the ruling Communist Party's official newspaper, said on Thursday.

Two people were injured during the demonstration on Sunday against a chemical plant in the southern city of Maoming, the newspaper's investigation found. No one was killed.

It said a small number of "criminals" set fire to a police car and destroyed storefronts and advertisements. Reports of armoured vehicles entering the city were false, it said.

Hong Kong media reported another demonstration over the plant on Thursday, with about 20 people protesting in the nearby city of Shenzhen. The reports said the protesters were quickly taken away in police cars.

Protesters have told Reuters that they saw several people killed in the weekend protests in Maoming and that dozens were injured.

The demonstrations spread to the provincial capital of Guangzhou on Tuesday, where police detained eight demonstrators, but they were released by Wednesday evening, sources with direct knowledge of the matter said.

One of those detained, reached by telephone, said none had been charged with any crime.

"We never had any physical conflict with the police," she said. "There was really no reason to charge us with any crime."

They were held for 24 hours at a police station, she said, adding that she regretted joining the demonstration and believed she had been misled by violent images online of Sunday's protest.

Unverified photos circulating on Chinese social media early this week, later deleted by censors, showed demonstrators lying in pools of blood and ambulances taking away the injured.

The People's Daily said some of the photos posted online were not of the demonstration at all, but old news photos of a domestic spat.

An unverifiable video of Sunday's protest, obtained by Reuters, showed police in riot gear chasing protesters, wielding batons and firing tear gas. Images of the protests sparked a public outcry in China this week.

The protests are over a proposed plant to produce paraxylene, a petrochemical used in making plastic bottles and fabrics. It will be owned jointly by CNPC and Maoming's local government.