The southern coastline is being patrolled around the clock to prevent diesel from being smuggled into the country on fishing trawlers.

Vice Admiral Chatchawal Amrapal, commander of the Navy's Second Tactical Fleet, said maritime surveillance by both patrol boats and air reconnaissance along the eastern coast from Surat Thani to Narathiwat had begun earlier this week, after domestic consumers started feeling the pinch because of the fuel shortage.

Customs checkpoints in Yala and Songkhla, bordering Malaysia, have mobilised extra manpower to crackdown on smugglers.

The customs offices in Narathiwat, which administer both land and sea borders with Malaysia, are also patrolling off the coast.

The Energy Ministry's regional energy coordination office 12 director Pheeraphol Sakharin said supplies in the seven southernmost provinces were sufficient, and shortages were unlikely in the near future.

But Pheeraphol recommended motorists fill their vehicles at large petrol stations, which generally had a larger fuel quota than small or independently run stations.

In the northern province of Loei, the manager of a PTT petrol station said she was worried all the local PTT stations were going to run out of fuel.

She said most other suppliers had already run out, or would soon.

In Sakon Nakhon, some petrol station owners have had to wait two days to buy diesel from suppliers under a new quota system and many petrol stations have resorted to selling diesel at prices higher than legally allowed.

The price per litre at these stations is general at least Bt1 per litre more than it is at stations selling at regulated prices.

In Songkhla, many small petrol stations have shut because major suppliers have refused to sell them diesel. The owner of a petrol station in Hat Yai district said there would be no shortage during the Songkran holidays, but he could not tell what would happen after that.

In Chaiyaphum, operators of local bus services said they would soon have to hike fares because fuel had become so expensive.

"If the increase is not approved [by the government], the buses will have to stop running," said Adisorn Limphakdee, who owns a bus company in the northern province.