BANGKOK, THAILAND - Thai aviation authorities Thursday gave airlines the green light to use a naval base in the east of the country after protesters blocked off both of Bangkok's airports.

Several planes had already landed at the U-Tapao airbase following the seizure by demonstrators of Don Mueang domestic airport on Thursday and the main Suvarnabhumi Airport on Tuesday night.

"It's already begun," Chaisak Angkasuwan, director general of the Civil Aviation Department, told AFP.

"Many flights have landed there and I have authorised more than 20 airlines to utilise U-Tapao airport."

The protests have left more thousands of passengers stranded in the troubled kingdom, with around 3,000 of them having to spend the night in Suvarnabhumi before they were evacuted on Wednesday.

Chaisak said he had asked immigration and customs to reinforce their staff at U-Tapao, which is located in the eastern province of Rayong and operated by the Thai Navy.

Thai Airways International said its Bangkok-Los Angeles flight landed at U-Tapao early Thursday.