Prime Minister Prayut Chan-o-cha has assured Bangkok residents the government is trying to offset harmful dust levels over the city by calling on the help of artificial rain.

Bangkokians have been suffering as a result of ultra-fine dust since early this month when the Pollution Control Department issued warnings that levels had soared to 94 microgrammes per cubic metre of air in some areas -- far above the safety limit of 50 µcg.

Pollution was at dangerous levels early on Wednesday over most of the city.

"I don't want people to panic," Gen Prayut said on Tuesday, adding that the problem is affecting a number of other counties as well as Thailand.

One immediate measure the government is carrying out is using artificial rain to bring down dust levels.

That should bring some relief, at least in the short term, the prime minister said.

The Department of Royal Rainmaking and Agriculture Aviation started studying weather conditions to make artificial rain early this week, but factors such as humidity and cloud do not help, department chief Surasi Kittimonthon said.

The latest inspection was conducted on Tuesday northeast of Bangkok. Officials plan to make rain there and let winds carry rain clouds over the capital.

However, humidity was below 60% and cloud conditions were unsatisfactory. "The cool weather also adds to air pressure, which causes problems," Mr Surasi said.

The department will continue to check the weather every day and hopes to make rain as soon as possible, he said.

Haze warnings in Bangkok are rare when compared with the north of the country, where field-burning and bushfires are common. But the city is at greater risk during cool periods.

Fumes from vehicles on congested roads and from construction sites and factories are also believed to cause clouds of smog that contain dust known as particulate matter (PM2.5).

This can easily enter the lungs if people have no adequate protection.

It is a good idea to wear face masks, the city's Health Department chief Chawin Sirinak recommended.

His department also suggested people avoid doing exercise in areas where high levels of dust are reported.