TAIPEI -- Smog is likely to continue to shroud southern Taiwan into the weekend, after the island Wednesday experienced its worst air pollution since August this year, the island's environment watchdog said Thursday.

Most of the island was subject to high levels of PM2.5 on Wednesday, including northern Taiwan, which usually boasts clean air.

The Air Quality Index continued to flash orange at six monitoring stations in southern Taiwan Thursday, including Yunlin, Chiayi, Tainan, Kaohsiung and Pingtung, which means air quality in those areas remains unhealthy.

Air quality reached a level posing a threat to sensitive groups in 12 monitoring stations in those areas.

The smog is mainly a result of weak winds and other weather conditions, which make particles in the air hard to disseminate, an official said.