"It works well and weather conditions in Chiang Mai are better than in the last few days. It is still cloudy, but the sky is clearer now," Somchai Ruangsuttinaruparp, director of the regional rainmaking centre, said by telephone from Thailand's second largest city.

"We have to keep doing this until the situation is back to normal," he added.

The region has not seen rain since November in what has been an unusually long and dry cool season in Thailand.

Smoke from burning fields and forests in Thailand, neighbouring Laos and Myanmar has poured into valleys in the hilly region as a cold front prevented it from escaping into the atmosphere.

But the air quality in Chiang Mai had improved in recent days following efforts by fire fighters to put out forest fires and burning stubble, environment officials said.