None of the 270 passengers and 21 flight crew on board were injured.
Mr Sorajak denied initial media reports that one of the plane's tyres had exploded on landing.
"The plane's tyre did not burst or explode, but the left and right front tyres had low pressure," he said.
Crew members discovered one of the two front tyres was under-inflated shortly after the twin-engine Airbus 330-300 took off from Kolkata at 2.48am Thai time.
The crew members requested permission to make an emergency landing as they approached Suvarnabhumi airport, the flight's destination, at about 6am, Mr Sorajak said.
After the plane landed, ground crew found the other main tyre at the front of the aircraft was also under-inflated.
The tyres were replaced and the plane was towed to the airport gate where passengers disembarked at about 8.15am.
"The aircraft had to be inspected in accordance with international standards before leaving [Kolkata] airport, so THAI will now investigate the cause of the under-inflated tyres," Mr Sorajak said.
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