Chinese police believe a nationwide food safety campaign they launched in August has effectively curbed the illegal practice of making and selling "gutter oil."

Officers with the border defense detachment in Nantong, East China's Jiangsu province, show local residents on Sept 28 how to identify gutter oil.[File photo]

Between the launch of the campaign and November, over 700 suspects had been detained during the investigation of 128 cases in 28 provinces and municipalities, according to a statement from the Ministry of Public Security issued on Monday.

The number of cases emerging dropped substantially in the three consecutive months, said the statement.

The statement also highlighted that 60 major gutter-oil-producing networks had been cracked, with most of them conducting cross-provincial operations.

However, the ministry assured the public it would keep up pressure on those flouting food safety laws and seek to establish "permanent mechanisms" to address these issues.

Food safety has become a growing public concern in China following a string of scandals over recent years.

"Gutter oil" commonly refers to produce illegally made by reprocessing waste oil from restaurants.

Such oil could otherwise legally be used in making biodiesel fuel or animal feed in China.

In the statement, the ministry revealed that firms in those legal businesses had seen a growth in the volume of "raw materials" they collected as a result of the campaign.