ATHENS: Alexis Tsipras was sworn in Monday as Greek prime minister at the helm of an anti-austerity coalition after an election win that has sent shockwaves through Europe.

Tsipras's radical leftwing Syriza party cruised to victory in Sunday's vote, setting the country on a collision course with international creditors over plans to renegotiate its massive bailout deal.

Syriza took 149 out of the 300 seats in parliament, becoming the first party to take power in Europe that openly rejects spending cuts and austerity measures.

Tsipras - characteristically wearing an open-necked shirt without a tie at his investiture - also broke with tradition by taking a civil instead of a religious oath.

The 40-year-old former Communist youth activist pledged to "always serve the interests of the Greek people" as he became the country's youngest prime minister for 150 years.

Having fallen two seats short of an absolute majority, Syriza quickly forged a coalition with the small right-wing Independent Greeks (ANEL) party.

Tsipras' first priority will be to deliver on his pledge to renegotiate the terms of the country's massive 240-billion-euro ($269 billion) EU-IMF bailout despite universal opposition from Greece's European allies.

Renewed fears that Greece could be forced out of the eurozone if it defaults on its debt repayments saw the euro hit an 11-year low against the dollar while Greek stocks closed down more than three percent.

Tsipras said Sunday his victory would see Greece "leaving behind disastrous austerity".

Syriza mocked claims by former prime minister Antonis Samaras' New Democracy party that the country would grind to a halt if it elected the radical left-wing party.

"The sun is shining, the bank cash dispensers are working and people are at work," said party spokesman Panos Skourletis.

'Change for better'

Many Greeks were optimistic that the fortunes of a country mired in deep recession for six years were about to change for the better.

Nikos, a Syriza supporter in Athens, said: "Today is a very good day. I believe things will go well for our country."

But other Greeks were sceptical.

"There are many promises, but at the end there will be nothing. They only want power," said Athina Mantsinou as she walked through the capital's Syntagma Square - scene of many demonstrations against austerity. Thousands of people had poured into the streets of Athens on Sunday, partying through the night after Syriza's bigger-than-expected win.

As supporters waved the party's red and white flag, Tsipras said Syriza's victory was a "mandate for national rebirth" after the "humiliation" of years of painful austerity.

But in a sign of the mammoth challenge ahead, the EU issued a stern warning to Greece that its place in the eurozone would be at risk if it failed to meet its austerity and debt commitments.

From Brussels to Berlin officials said they were open to talks with the new team in Athens, but many signalled its proposals were unrealistic.

In exchange for the bailout in 2010, Greece was forced to slash public sector spending, cut wages and pensions and introduce a far-reaching programme of privatisation. Syriza has pledged to reverse many of those measures.

But Chancellor Angela Merkel of European paymaster Germany made her views clear.-AFP