Voting has begun in Greece's general election, with opinion polls indicating a tight race between the left-wing incumbent Syriza party and the conservative New Democracy.

The snap election, Greece's fifth in six years, was called after Syriza lost its parliamentary majority in August.

Syriza leader Alexis Tsipras's popularity plummeted after he agreed a new bailout deal with European leaders.

The bailout involved austerity measures which Syriza had vowed to oppose.

Greece is mired in a deep financial crisis and whoever wins Sunday's election will have to oversee further tough economic reforms.

The BBC's Richard Galpin in Athens says whichever party wins is unlikely to get enough seats to form a government alone.

That could mean a period of political instability just as deadlines loom for the implementation of a series of key financial reforms, he says.

Analysis: Richard Galpin, BBC News, Athens

Most opinion polls indicate the conservative party New Democracy and Syriza are running very close.

But unlike last January's election, there is little excitement about Sunday's vote; campaigning has been lacklustre and the response of the electorate muted.

Syriza's high noon has passed, the party and its leader bruised by their experience in government.

Tsipras's decision to abandon the anti-austerity stance which had propelled him into government, and instead sign a bail-out deal with Greece's European creditors, fractured Syriza, with 25 MPs setting up their own parliamentary party.

Tsipras signed the bailout deal shortly after a referendum in which more than 60% of voters rejected the austerity measures creditors wanted to impose.

In interviews leading up to the election,  Tsipras said he had put his country above his party. He said that had he not agreed to the three-year bailout, Greece would probably have had to leave the eurozone.

He told Antenna TV on Friday he would "tug the rope" to try to win relief on Greece's huge national debt from EU creditors.

New Democracy leader Vangelis Meimarakis has dismissed  Tsipras's term in office as "an experiment that cost [the country] dearly".

"I fear that if Syriza is elected... the country will soon be led to elections again, and this would be disastrous," he said.

Commentators say there is also a tight race for third place between the socialist Pasok party and the far-right Golden Dawn.

Analysts have said the migrant crisis on Greece's doorstep may boost support for Golden Dawn, which is strongly opposed to immigration.

Polls close at 16:00 GMT, with the first projected results expected two hours later.