Kuala Lumpur and Singapore have ranked among the world’s most polluted cities as haze from Indonesian wildfires chokes Southeast Asia.

Kuala Lumpur topped the global ranking early on Wednesday with an Air Quality Index reading of 166, according to Swiss monitor IQAir. Singapore ranked third at 155. Readings above 150 are classed as unhealthy.

AFP reported that smoke from wildfires on Borneo and Sumatra has shrouded the cities for more than a month. Hot, dry El Niño conditions have fuelled the fires.

Residents say the haze is hurting health and visibility. In Kuala Lumpur, a 22-year-old graduate said she could not even see the Merdeka 118 tower through the smog.

Transboundary haze is a recurring problem in the region. This year’s episode has been severe, with land-clearing fires making the blazes harder to contain.

The haze returns almost every dry season in Southeast Asia. Indonesia’s peatland fires are the main source of the smoke. Governments have pledged action for years with limited success. Schools have closed during past episodes. Until the fires are controlled at source, the region faces the same choking air each year.