State media say police in a northern Chinese city have broken up a major toxic waste case that came to light when a restaurant owner died after inhaling poisonous gases coming from his kitchen drain.

The official Xinhua News Agency said Monday that police discovered that the operator of a parking lot near the restaurant in Baoding city had allowed factories to dump highly toxic waste into its drain pipes for illegal gains.

Xinhua said the parking lot operator allowed a total of more than 3,400 tons of toxic waste to be dumped between August 2014 and May 2015.

It said police arrested 27 suspects and that 20 factories were implicated in the dumping.

Pollution is a severe problem in China, and factories often break environmental laws.