Greek conservative leader Kyriakos Mitsotakis has trounced his centre-left rival in the second election in a month and said he has a "strong mandate" to move faster on the path of change.

His New Democracy party (ND) won 40.5% of the national vote, almost 23 points ahead of Alexis Tsipras's Syriza party.

He beat Syriza in May, but called new elections in a bid to win a majority.

"ND is today the most powerful centre-right party in Europe," he told delighted supporters in Athens.

Mr Mitsotakis, who was sworn as prime minister on Monday, is credited with successfully returning the Greek economy to stability and growth after a severe debt crisis and three international bailouts.

Although many Greeks are struggling with the cost-of-living crisis, voters chose to stick with the party promising lower taxes and improved public health.

The vote came 11 days after a migrant boat tragedy off Greece in which about 500 people are thought to have died.

Three days of mourning were held, however the disaster had little effect on the campaign and Greeks voted to maintain economic stability.

"The people have given us a safe majority," said Mr Mitsotakis as the extent of his victory became clear. "Major reforms will go ahead quickly."

Last month, his party fell just short of a majority in the 300-seat parliament and his decision to call an election in a bid to form a stable, single-party government was vindicated by Sunday's result.

Under Greek rules for a second election, the biggest party is awarded a bonus of between 20 and 50 seats. With more than 40% of the vote, New Democracy won all 50.

Mr Mitsotakis said he could not promise miracles, but that New Democracy had "high goals" to transform Greece with a better public health service and education.

Former Prime Minister Alexis Tsipras's centre-left Syriza had been soundly defeated in the first election and lost further ground in the second, with less than 18% of the vote. He dampened speculation that he would resign, saying that was a decision for his party members.

One of the big stories of the election was the success of a newly created far-right Spartans party, which won almost 4.7% of the vote, crossing the 3% threshold to enter parliament.

The Spartans only emerged as a political force this month when the Supreme Court banned another far-right party, the Greeks, and its jailed founder, Ilias Kasidiaris, threw his weight behind the Spartans.

Kasidiaris had been the spokesman for neo-Nazi party Golden Dawn, which was banned as a criminal organisation and its leaders given long prison terms.

Together with nationalist Greek Solution and ultra-conservative Niki (Victory), the three hard-right parties won close to 13% of the vote and 34 seats.

The victory secured by Kyriakos Mitsotakis, 55, over Alexis Tsipras's Syriza is a rarity in Greek politics, as few parties increase their share after a first term in office.

He also succeeded in attracting more young voters than his rival.

His party was helped by the fragmentation of the left-wing vote; with Socialist PASOK set for more than 11% and the Communist KKE on around 7%.

Turnout slumped eight points from the first vote to less than 53%.

The conservative leader has formed a reputation as a Teflon-coated leader, fending off a series of damaging crises in the past year, including a rail disaster and a wire-tapping scandal that brought down the intelligence chief and his own nephew, who worked as the prime minister's chief of staff.

Greece was being led by a caretaker government when the migrant boat sank off the south-west coast in the early hours of 14 June.

Since the migrant crisis, the views of most Greek voters have shifted in favour of stricter, more conservative policies, says Panos Koliastasis, assistant professor of politics at the University of Peloponnese.

"The reason is rooted in the 2020 migration crisis on the Evros [river], when Turkey tried to push thousands of migrants into Greek territory and the Mitsotakis government acted swiftly. So the greater part of the public perceives the migration issue as an external threat to national sovereignty."