File photo: CGTN

ISTANBUL, March 25 (Xinhua) -- At least four workers were wounded in an explosion at an oil refinery in northwest Turkey, local media reported on Friday.

The blast occurred at the Turkish Petroleum Refineries Corporation (TUPRAS)'s facility in the Kocaeli province, about 100 km to the country's largest city Istanbul, reported the Ihlas news agency.

It said the cause of the incident, which happened at one of the filling tanks of the refinery, was not immediately clear, and authorities launched a comprehensive investigation.

The injured have been rushed to nearby hospitals, the report said.

A fire broke out after the explosion and was extinguished in a short time, it added.

TUPRAS operates four refineries across the country, and the refinery in Kocaeli processes 11.3 million tons of crude oil per year, accounting for 33 percent of Turkey's petroleum products consumption.