Lawrence Wong said in a Facebook post late on Thursday, 'we are looking into which companies may be responsible for the fires.' (EPA Images pic)SINGAPORE: Singapore Prime Minister Lawrence Wong has vowed to take action against companies found responsible for fires in neighbouring Indonesia that have plunged the region into an air pollution crisis.

The pledge comes as smoke from Indonesian wildfires blankets parts of Southeast Asia, closing schools and fuelling a surge in respiratory complaints across the region.

The city-state topped IQAir's live ranking of the world's most polluted major cities again early Friday, with Jakarta second and Kuala Lumpur fifth.

"We are looking into which companies may be responsible for the fires," Wong said in a Facebook post late Thursday.