Authorities in a southern Chinese city grappling with protests against plans to build a petrochemical plant have detained eighteen protesters, local police said Thursday.

Since Sunday, more than 1,000 residents of the town of Maoming have held protests against the plant that is expected to manufacture paraxylene (PX), as many fear the plant's effect on the environment and on the health of local residents.

The local Public Security Bureau?said during a news conference Thursday afternoon that it had imposed administrative punishments on 26 people, in addition to detaining the 18 others.

The police said the detained protesters were charged with "assembling a mob to disrupt social orders," and also said that they had not detained or punished any students.

Maoming, which has a population of 7 million, already boasts the largest petrochemical base in southern China.

Since 2007, planned PX projects in Xiamen, Dalian, Ningbo and Kunming have been canceled after residents protested. It is not yet clear if the Maoming government will follow suit.

Chang Yizhi, a chemical industry researcher with CIConsulting, a leading Chinese industrial consultancy, said China was the world's largest consumer of PX in 2013, and the country consumed 16 million metric tons of the chemical – with more than half imported from overseas.