Thick smog enveloped Malaysia’s Johor state as plummeting air quality forced more than 200 schools to shut down.

Malaysian authorities ordered dozens of schools in the southern state to temporarily close and banned open burning in some areas as pollution from forest fires in Indonesia continues unabated.

Muar, a town off Malaysia’s southwestern coast across the narrow Strait of Malacca, was hit hard by smoke from the fires. Other towns in Johor state were also cloaked in hazardous haze and schools could remain closed until Monday.

Malaysia’s Department of Environment expressed concerns about the thick smoke blowing over the border that has been pushing air quality to “unhealthy” levels and urged Indonesia to ramp up efforts to douse the flames in central Sumatra.

Over in Singapore, smog worsened to the highest on record Thursday, with the city-state’s three-hour Pollutant Standards Index rising to a hazardous level of 371.

Indonesia said it was doing its best to rein in the haze problem, which could strain relations between the Southeast Asian countries.

“From 850 hectares, we have managed to put out the fire in 650 hectares of peatland,” in Riau province, central Sumatra, said Indonesia’s Coordinating Minister for Social Welfare Agung Laksono.