Supporters of Thai prime ministerial hopeful Pita Limjaroenrat rallied ahead of a critical parliament vote that would determine Thailand's next leader.

Liberal Move Forward Party members gathered in Nakhon Ratchasima province on July 12, a day before conservative pro-establishment senators were set to decide on the country's premiership on July 13.

Major Winai Saitangjai, 61, a volunteer leader for the party, said that Pita's supporters will be rallying in Bangkok today, July 13, or watching the parliament vote at two meeting venues in the province.

He said: 'July 13 will be an important day for Thai politics because it is the day that the new prime minister will be selected.

'I believe that all Nakhon Ratchasima residents will be watching closely, as the previous election saw over 1 million people, or almost all of the electorate, vote for either the Move Forward Party or the Pheu Thai Party.

'I am optimistic that the prime minister selection will go smoothly and that Pita will be 100% selected as the prime minister.'

He added that he hoped that the senators - many of whom are pro-establishment - have the maturity to follow the 'will of the people' and 'help Thailand progress politically.'

Winai said: 'Only a few senators have stated that they will not vote for Pita. If he does not become prime minister, it will cause chaos.'

The Move Forward Party won the most seats in a national poll on May 15.

However, a junta-appointed cabal of 250 'senators' handpicked from the country's benighted institutions will now cast the deciding votes on which party can govern - rendering any elections a sham.

The ultra-conservative senators - branded 'dinosaurs' by critics - have pledged their loyalty to protecting the monarchy and vowed to prevent the Move Forward party from entering government due to its stance on modernising the state and watering down the Lese Majeste law, which they see as a threat to national security.