China's eastern city of Ningbo detained more than 50 people over violent protests last week that successfully blocked a planned chemical plant, state media said Tuesday.

Ningbo city said Sunday that work on the 55.9-billion-yuan ($8.9 billion) oil and petrochemical complex would stop after thousands of local residents clashed with police in a week-long protest over pollution fears.

Police detained 51 people who clashed with police last Friday, throwing stones and overturning two vehicles, the Ningbo Daily said Tuesday.

Of the 51, 13 were deemed criminal suspects, the newspaper said, meaning they could face prosecution. Police could not be reached for comment on the report.

Authorities detained another man, who was found carrying a knife, during protests on Sunday evening, said the report, which quoted Ningbo city officials.

Separately, authorities also detained a woman for spreading false rumours that a university student died in the protests, police said in a separate statement.

Environmental pollution has increasingly sparked protests across China, helped by social media, which allows organisers to publicise their causes and rally others despite tight controls in the one-party state.

Ningbo residents told AFP that the protests had tapered off on Tuesday after the government's pledge to halt the project, despite suspicion the city might try to revive it, but the police presence remained strong.

"The streets are full of patrolling police cars," said a resident of Zhenhai, which was the proposed site of the plant.

Zhenhai district said Sunday it would "ban" production of paraxylene (PX), a petrochemical used for plastic bottles, which had been the focus of residents' health fears.