BANGKOK — More than 400 schools in Thailand’s capital, Bangkok, were shut Wednesday for the rest of the week due to increasing concern over dangerously unhealthy air pollution.

Faced with public discontent as well as a possible health crisis, Police General Asawin Kwanmuang, the city’s governor, also declared the city a ‘‘pollution control zone,’’ allowing authorities to take legal measures to combat the threat, including road closings and diversions. Violators of orders to curb pollution, which could include limits on diesel exhaust, outdoor burning, and construction activities, could face up to three months in prison.

Prime Minister Prayuth Chan-ocha directed Asawin to order the closure of 437 schools after officials said the pollution would continue until next Monday. They said still air and heavy traffic are causing a buildup of particles in the air.

The Pollution Control Department said the amount of especially dangerous tiny ‘‘PM 2.5’’ particles has risen in all areas in and around Bangkok since Monday.

‘‘We decided to eliminate the problem by closing down the schools,’’ Asawin said. ‘‘We’re afraid that it can be dangerous for the children.’’

The Public Health Ministry said people should refrain from outdoor activities and exercise, and look instead for indoor venues.

Many commuters and pedestrians have begun wearing face masks.

Pollution levels also rose elsewhere in Thailand, bringing a heavy haze to Chiang Mai and other northern areas well ahead of the annual ‘‘smoky season’’ that normally begins in late February.

associated press