Mr Somchai cast his ballot at a polling unit at Krungthep Kanbanchi School in Bangkok. He invited all eligible voters to exercise their election right. All polling units are set to close at 3pm.
Supachai Somcharoen, the EC chairman, exercised his voting right at polling unit No 17 in tambon Bang Kruay of Bang Kruay district in Nonthaburi province.
Reports said Abhisit Vejjajiva, the Democrat Party leader, who is supposed to turn up to vote at polling unit No 4 at Sawasdee School in Soi Sukhumvit 31, may not be able to do so because he is sufferring from a fractured collarbone.
Caretaker Prime Minister Yingluck Shinawatra is expected to turn up at about noon to vote at polling unit No 32 at Khlong Lamchiak School in Bung Kum district.
Pol Lt Gen Aree Onchit, an assistant national police chief, said about 100,000 police have been deployed to provide security at all polling units nationwide.