Greece's struggling main opposition Syriza on Thursday was hit by fresh defections with nine departing lawmakers accusing rookie leader Stefanos Kasselakis of destroying the party through authoritarian behaviour.

The defectors, who included several senior members and ex-ministers, accused Kasselakis of "undemocratic" behaviour that they said was "destroying" a party which headed Greece's first leftist government in 2015-2019.

Syriza now has 36 lawmakers in the 300-seat parliament, just four more than the socialist Pasok party.

The exodus began on November 12 with the departure of former finance minister and MP Euclid Tsakalotos -- who helped navigate Greece out of its debt crisis and EU-IMF bailouts -- and another lawmaker.

Over 40 party members quit alongside Tsakalotos and dozens more joined them this week.

A former Goldman Sachs trader, 35-year-old Kasselakis was the surprise winner of a party leadership race in September that followed successive Syriza defeats in elections this year, prompting the resignation of longtime leader Alexis Tsipras.

A political novice, Kasselakis had pledged to create a "modern Left" that can win back power.

Syriza has plummeted in opinion polls following Kasselakis' election and is lately shown falling to third place.