Thailand's parliament opened Thursday to vote for a prime minister, with frontrunner Pita Limjaroenrat insisting he was confident of victory despite a barrage of last-minute hurdles that could undo his premiership bid.

It is a pivotal moment in the dramatic aftermath of his progressive party's shock May election win, with fears for renewed political instability in a country that has seen over a dozen military coups in the last century.

To win, Pita needs support from at least some members of the country's more established parties and junta-appointed senators, who were spooked by his Move Forward Party's victory and horrified by its plans to amend the kingdom's strict royal defamation laws.

Complicating his path to top office further, Pita faces the threat of parliamentary suspension, and two cases that have been filed against him and his party.

He was nonetheless bullish ahead of Wednesday's session, where lawmakers will debate for long hours before beginning to cast their votes.

"I am confident in myself that I will work with my full capacity to respond to people's hopes and the support that they gave to me," Pita told reporters ahead of the session opening.

"I will try my best to show my vision, explaining to all the senators' doubts."

As the session began, the streets approaching parliament were empty of people, and razor wire could be seen on highway overpasses.

Containers covered by tarpaulins decorated with images of Thai landmarks ringed the parliament compound perimeter.