A record 50 flights were cancelled on Thursday due to thick smog from forest fires in Indonesia covering the southern provinces.
Tinnagorn Choowong, executive vice-president of Aeronautical Radio of Thailand (Aerothai), said the thick layer of haze had forced airlines to cancel 50 flights at five airports.
These were Hat Yai, Trang, Surat Thani, Nakhon Si Thammarat and Koh Samui airports.
The cancellations were the highest number seen in the country to date.
Koh Samui airport was the worst affected, Mr Tinnagorn said.
Carriers announced flight cancellations after 4.30pm after the thick haze reduced visibility to around 1,000 to 3,000 metres, from the standard 5,000 metres.
Mr Tinnagorn said the navigation system at Koh Samui airport could only cope with a minimum visibility of 1,500 metres.
This meant the taking off and landing of aircraft would mostly depend on pilot visibility, he said.
The five airports and Aerothai have been closely monitoring the haze situation and the weather via the Thai Meteorological Department, Mr Tinnagorn said.
They have been providing updated information to carriers, he added.
Meanwhile, haze eased on Friday in Songkhla, Yala, Pattani, Satun and Surat Thani provinces.
The let-up followed rainfall and a change in wind direction in the Gulf of Thailand due to a high-pressure system from China.
However, dust particles remain above the safety threshold of 120 microgrammes per cubic metre, which poses a significant risk to health.
In Songkhla, the level of smog particles dropped to 260 µg/cu m after surging on Thursday to 360 µg/cu m — the most harmful level the country has experienced.
Hat Yai airport resumed operations after the haze eased.
In Pattani, the airborne particle level also dropped.
However, local authorities, led by Pattani governor Weerapong Kaewsuwan, pressed on with distributing face masks to residents in Muang municipality.
Dr Banjerd Sookpiphatpanon, a Pattani health office chief, also instructed medical teams at local hospitals to prepare for patients seeking treatment due to the smog.
In Narathiwat, the haze resulted in a drop in passenger numbers on a ferry service between Thailand and Malaysia at Taba checkpoint in Tak Bai district.
Santhana Chanthorn, marine chief of Narathiwat, said the heavy haze conditions had caused poor visibility at sea.
He said the number of commuters fell from 30 per trip to just five or six as people had decided not to travel for their own safety.
Mr Santhana also warned boat operators to exercise extra caution when putting to sea.
Small boats should refrain from leaving shore for the time being and fishermen should closely monitor the weather forecasts, he advised.
Meanwhile, Interior Minister Anupong Paojinda said schools in the southern provinces were allowed to close temporarily if the smog particle level rose above 350 µg/cu m.
Gen Anupong also ordered provincial health offices to work closely with schools to monitor the haze situation.