Dense clouds of dangerous toxic smog suffocated Bangkok’s air on Monday, forcing residents to seek shelter inside and wear special masks, Business Insider reports.

The thick smog — which is caused by a mix of ultra fine dust particles emitted from vehicles and construction sites and high humidity levels — has grown so bad in recent years that some of the nation’s highest officials are considering moving the capital entirely.

The dust particles, which are known by the identifier PM2.5, are thin enough to enter a person’s bloodstream if they breathe them in. Once inside the body, the pollutants can lead to respiratory and cardiovascular illnesses.

Massive overcrowding, traffic congestion, and lackluster regulations have all played a major role in Bangkok’s pollution woes, leading some major officials, including prime minister Chan-o-cha, to float the idea of moving the capital entirely. Chan-o-cha hinted at the possible relocation effort during an address to the World Conference earlier this month.

“The first is to find a city that’s neither too far nor too expensive to move to,” Chan-o-cha said. “The second is to move to outer Bangkok to reduce crowding.”

The prime minister stressed that more research is needed before the government officially decides to move to the outskirts of Bangkok but said it’s possible such a move could happen under his administration.

More at Business Insider