GREEK left-wing opposition party Syriza suffered a major setback today when nine lawmakers quit the party in protest against its newly elected leadership.

Miami-based businessman Stefanos Kasselakis stunned party veterans when he won the leadership in late September in a primary-style contest. 

But he has failed so far to halt the party’s decline in popularity in the wake of a crushing general election defeat in June.

Syriza has since dropped to third place behind socialist opponents in opinion polls, boosting the dominance of Prime Minister Kyriakos Mitsotakis’s conservative government.

On Thursday, Effie Achtsioglou, a former Syriza labour minister, led the walkout as nine lawmakers declared themselves to be independent.

They joined former finance minister Euclid Tsakalotos and another colleague who quit on November 11, reducing the number of seats held by Syriza in the election from 47 to 36 in the 300-member parliament.

Critics of the new leader have described him as intolerant of dissent and unable to reach a policy consensus.

The Communist Party of Greece has roughly doubled its support over the last four years to reach 10 per cent in recent polls.

In a party statement, Syriza said that many of the dissenters had ignored repeated and public invitations made by Mr Kasselakis to join him in reforming the party.