Northern tourism operators expect a poor showing during the Songkran holiday as the region remains choked by smog, amid weak spending attributed to the war in the Middle East and the subsequent oil shock.

This week Chiang Mai ranked as the most polluted city in the world, while other northern provinces such as Mae Hong Son continue to suffer from smog caused by wildfires.

The Chiang Mai Chamber of Commerce said forward bookings for the province have been very slow and the Songkran holiday might not be as high as last year.

Concerns about smog and rising oil prices are influencing tourists' decisions.

Many Thais, foreign visitors and expatriates may choose seaside destinations instead, leaving only locals in the North or business operators who need to visit the city, the association said.

The occupancy rate in Chiang Mai has hovered at 30-40% after the smog started, it said.

Operators are reluctant to increase their room prices and service fees despite rising costs.

The smog this year is mainly caused by wildfires and cross-border fires, the association noted.

It said authorities in the northern provinces must collaborate in order to address smog issues, as a fire occurring in one province can impact the air quality in another.