Greece’s conservative opposition chief Antonis Samaras has announced his resignation after the country was on course to soundly reject further austerity cuts in a referendum.

"I understand that our great movement needs a new start.

From today I am stepping down from the leadership," the New Democracy chief, a former prime minister, said in a televised address on Sunday.

Samaras, 64, had faced calls to resign in January after his party was beaten in national elections by the radical leftist Syriza party of Prime Minister Alexis Tsipras.

Samaras’ term was originally to end in 2016, but his fragile coalition failed in December to elect its candidate for Greek president, triggering an early ballot.

The New Democracy party had campaigned for a ‘Yes’ result in Sunday’s referendum, echoing warnings from European officials that a rejection of EU-IMF reform proposals could see Greece crash out of the eurozone.

An official tally of over half the ballots cast showed a resounding 61 per cent of Greek voters had backed the ‘No’ in the plebiscite, as called for by Tsipras’ government.