The fishing industry has become the latest to face a crisis from the shortage of diesel and the high cost of black market supplies, with about 2,000 fishing trawlers operating in the Gulf of Thailand forced to stay in port.

The crisis has already affected road transport operators, who have called for an increase in fares.

The head of a fishery association in Pattani said there would soon be another 200 to 300 trawlers docked as operators could not shoulder the higher operating costs.

"We will wait and see depending on the diesel price," said Wiroj Janimi.

A representative of the Songkhla fishermen warned the problem would soon be critical and called for immediate government action, whether it be price intervention or subsidies.

Praphorn Ek-uru said fuel prices were the crucial factor to the fishery industry and would have a direct impact on fish and seafood catches.

"It will cause a chain reaction to the processed and frozen food industries and subsequently the export sector," he added.

He said 500 trawlers operating from Songkhla's piers had completely ceased their operations.

The government subsidy scheme, known as "purple oil", in which cheaper diesel is sold to trawlers, has largely benefited smaller operators because the distribution points are far from the deep-sea locations where large vessels head, he said.

About another 1,500 trawlers that operated off the Surat Thani coast have remained in dock for long periods.

Anan Choosak, chairman of the provincial fishery association, said crews working aboard many small trawlers that could not even afford to buy the cheaper purple oil have turned to other jobs.

For use with vehicles, several petrol stations in Nong Khai limit the sale of diesel to just Bt500 a vehicle while smaller stations sell at unlimited amounts but at a higher rate of Bt28 per litre.

Passengers travelling to the provincial airport on chartered buses have been charged another Bt20 on top of the Bt100 fare.

In Chiang Mai, many petrol stations stopped selling diesel, citing shortages. The head of the provincial trade office said she would investigate whether stations were hoarding oil.

Fuengfa Tulathammakul said fuel hoarders could face seven years in prison and fines of Bt140,000.

The shortage has also prompted small passenger trucks to modify their vehicles to run on cooking oil (liquid petroleum gas, LPG).

Singkham Nanti, head of the Lanna Motoring Cooperative, said the so-called "red four-wheeled trucks" equipped with LPG used only half the amount of diesel.

More than 1,000 two-row passenger trucks in Khon Kaen will probably increase fares this week because of the high prices. Bunkern Phimworramethakul, an adviser to the Khon Kaen Motoring Cooperative, said his group was lucky that it could still buy diesel from the PTT storage agent, albeit at higher prices.

He said many members of the cooperative, who run independent services, had opened petrol stations or storage tanks to store oil that had been bought in large quantities.

Operators of private buses and vans will meet Deputy Transport Minister Chaiyanan Charoensiri to discuss their renewed demand for a fare increase after the price of diesel rose above Bt24.50 per litre.

Sujinda Cherdchai, Private Bus Operators Association president, said after the oil price went beyond the Transport Ministry's promised ceiling of Bt24.50 per litre to the current price of Bt24.69, bus operators decided it was time to meet Chaiyanan.