Firefighters in the southern Indian city of Kochi scrambled on Tuesday to control the spread of toxic fumes after a landfill fire broke out five days ago, blanketing the area in thick fog and suffocating residents.

The massive Brahmapuram landfill in Kerala state is the latest fire incident in the country’s “garbage mountain”, causing dangerous heat and methane emissions and adding to India’s already mounting climate challenges.

Authorities advised the city’s more than 600,000 residents to stay indoors or wear N95 face masks if they needed to go out. Additionally, schools were forced to close on Monday as a result of the pollution, officials said.

The fire broke out last Thursday, according to the Kerala Fire Service. The cause is undetermined, but landfill fires can be caused by flammable gases rising from garbage.

While the fire has been largely extinguished, a thick cloud of smoke and methane gas continues to cover the area, reducing the city’s visibility and air quality, while emitting a strong odor.

Some firefighters had passed out from the fumes, the fire department said.

The Kerala high court said it will hear the case on Tuesday.