Authorities have continued to search for victims and survivors of a trawler that sank off the coast of Greece with as many as 750 refugees on board, as conservative leader Kyriakos Mitsotakis blasted critics of the rescue operation.

Naysayers, Mitsotakis said at a campaign stop in the town of Sparta on Saturday, should turn their ire against traffickers he called "human scum."

The Greek coast guard announced on Saturday that one Greek Navy frigate and four other vessels were operating 87 kilometres southwest of the town of Pylos in Greece's southwest.

Earlier, two helicopters from the navy and coast guard joined the operation, the coast guard said. The rescue operation is taking place in rough seas, with near gale-force winds, and in some of the Mediterranean Sea's deepest waters.

To date, 104 survivors have been rescued and 78 bodies have been recovered.

The trawler carried as many as 750 men, women and children from Syria, Egypt, the Palestinian territories and Pakistan. No survivors or bodies have been found since the day of the accident.

The survivors have been taken to a refugee reception centre outside Athens. Greek authorities continue to face criticism, however, over their failure to act more quickly.

They say the refugees insisted they didn't need any help, but non-governmental organisations say they received a number of calls for help.

Mitsotakis rejects criticism

On Saturday, parts of the Greek rescue vessel captain's testimony were published by Greek media.

In it, he said the refugees refused help, saying they were going to Italy, and untied a rope loosely tied to the trawler's bow when the coast guard ship had gone closer to inspect.

"It is very unfair for some so-called 'people in solidarity' to insinuate that the [Coast Guard] did not do its job. ... These people are out there battling the waves to rescue human lives and protect our borders," Mitsotakis said.

Mitsotakis, the favourite to win a second four-year term in elections on June 25, attacked the main opposition party Syriza for its own record on migration while in government.

"Those who today appear as the so-called authentic humanitarians are those who allowed detention camps such as Moria to exist. The same who, a few days ago, were condemned by the European Court of Human Rights for the wretched conditions at Moria."

The notoriously overcrowded refugee camp of Moria, on the island of Lesbos, opened in January 2013 under a three-party coalition government led by New Democracy.

It saw its population swell during the migration crisis of 2015.

It operated throughout the Syriza administration from 2015-19 and burned down in September 2020.

Just before it did, it was estimated that 20,000 people lived in a camp designed to accommodate 3,000.

Mitsotakis also attacked Syriza for "opening the doors to millions of people" in 2015 and defended his own more restrictive policies, vowing to continue them.

"We followed a different migration policy ... fair and strict, of monitoring and guarding our borders. A policy which resulted in illegal crossings dropping 90 percent," he told the crowd.

"This policy has been acknowledged [by Europe] as the right one. Because if we leave Europe's borders to allow in everyone, then the numbers of those wanting to cross the Mediterranean will rise exponentially and so will the chances of tragic shipwrecks."

Lawmaker sacked for racist comments

Meanwhile, a right-wing Greek parliamentarian was expelled from Mitsotakis' party for racist remarks after the mass drowning of refugees.

While condemning the "tragic" loss of life, including "children", Spilios Kriketos, a lawmaker in Mitsotakis' party, said on Thursday that Greece "cannot tolerate more migrants", in an interview on the Kontra YouTube channel.

He then accused refugees of stealing.

On Friday, ND said it had expelled him.

"Opinions such as those expressed by Spilios Kriketos have no place in our party," the party said in a statement.

"Statements of hate and racism are not part of the party's values."