The UN refugee agency has cast doubt on reports several hundred people have died in a new migrant tragedy in the Mediterranean.

Unconfirmed media reports said there were 400 victims from boats that capsized near the Egyptian coast as they attempted to sail to Europe.

Italian President Sergio Mattarella appeared to confirm the incident, saying Europe needed to reflect in the face of "yet another tragedy in the Mediterranean in which, it seems, several hundred people have died".

But both the Italian and Greek coastguard said earlier on Monday that they knew nothing about the reported disaster, and the UNHCR tweeted that the information that hundreds had died appeared inaccurate.

The ABC's Europe correspondent James Glenday said there remained uncertainty about what exactly had occurred.

Italian Foreign Minister Paolo Gentiloni confirmed reports of many migrant deaths in Egyptian waters and said he was waiting for more details.

Mr Gentiloni said what was certain was there had again been a tragedy in the Mediterranean, exactly one year after hundreds of asylum seekers drowned off the coast Libya in April 2015.

The BBC reported it had spoken to asylum seekers in Greece who claimed they were on the ship that capsized, and that up to 500 people drowned in the incident.

Some of the survivors have reportedly been taken to one of the Greek islands, it said.

More than 177,000 asylum seekers have reached Europe by sea this year, with 723 people dead or missing, according to the International Organization for Migration.

ABC/Reuters