The 29-year-old victim, named only as Khith, was rushed to Pattaya Memorial Hospital after the incident in Bang Lamung district.
The explosion tore apart a Hainanese chicken rice restaurant on the ground floor and scattered kitchen equipment across the pavement.
Neighbouring shophouses also suffered damage in the blast.
Police cordoned off the scene and banned people from entering the shophouse over fear it may collapse. Officers picked through the wreckage and took photographs in a bid to trace the source of the accident.
Initial investigations pointed to a gas explosion.
Police estimated the damage at more than 1 million baht.
The building’s owner, named only as Paisan, 56, said he had rushed to the scene after getting news of the explosion.
He said that although the damage was severe, none of the gas cylinders stored at the restaurant had exploded.