NANJING - The blaze which followed an explosion on Monday in an oil refinery in the eastern Chinese city of Nanjing has not been extinguished, local authorities said Tuesday.

The Nanjing firefighting department told Xinhua that the fire has caused the collapse of three chemical storage tanks, and was still burning inside one of the tanks as of Tuesday afternoon.

The accident happened at around 12:40 pm on Monday when the sulfur recovery facility at the refinery of Sinopec Yangzi Petrochemical Co caught fire and exploded. The fire ignited three chemical storage tanks, and another of crude oil, which led to an explosion.

Qian Feng, deputy head of the city's environmental protection bureau, said that the chemical storage tanks also contained large volume of oil, which added difficulties to firefighting. The burning oil has released hydrogen sulfide.

Environmental examination shows the level of toxic gas in the area remains within national standard, but the air around the plant is still filled with a pungent odor.

A joint team comprising staff members from the city's firefighting department, the work safety supervision office and the public security bureau was set up to investigate the cause of the accident.