High arrivals, tighter borders and pressure on Greece where many are stranded prompt warnings of a looming crisis.
The United Nations has sent a team to Greece to investigate reports that hundreds of people may have drowned in the Mediterranean when a boat capsized.
Witnesses and survivors told Al Jazeera that a vessel carrying refugees and economic migrants sank on Monday, describing how they watched its passengers being swallowed by the sea.
Several unconfirmed reports and witness statements said that the number of dead could be 400 to 500.
The probe was announced by Ariane Rummery, UN refugee agency (UNHCR) spokeswoman, late on Tuesday. No government, navy, NGO or UN agency has been able to corroborate the witness accounts.
One of the survivors, Somali refugee Muhidin Ali Waash, said that the ship’s passengers rushed to one side of the vessel and “it lost balance”.
Asad Mohamed Othman, also from Somalia, recalled the incident.
“I can’t do anything because I am in danger, I am in the sea,” he told Al Jazeera in Kalamata, a Greek coastal city.
“My wife and my child are gone,” said Muaz Mahmoud Aymo, who left Ethiopia hoping to reach Europe.
Muaz said his wife, baby and brother-in-law all drowned.
“My family … three people in this boat … all dead,” he told Al Jazeera.
The UNHCR team was sent to Kalamata, where the local port authority has confirmed the rescue of 41 people from a wooden boat.
Rummery said, though, that there was no official confirmation of a link between the survivors and an incident such as the one described.
“We cannot confirm anything until we have a direct testimony or something from official authorities,” Flavio Di Giacomo, spokesman for the International Organisation for Migration (IOM), said.
Di Giacomo said that, according to some unconfirmed reports, a boat left Egypt and met a smaller boat that had sailed from Libya.
Passengers from the Libyan boat were then reported to have been moved to the Egyptian boat at sea.
If a vessel had capsized and hundreds of people had drowned, bodies may start washing ashore in Libya in the coming hours, Di Giacomo told the DPA news agency.
Somali government sources said that there could be up to 200 Somalis among those feared dead.
Officials from the Horn of Africa nation were trying to gather information through their embassies in Italy and Egypt, Foreign Minister Abdisalam Omar Hadliye said on Tuesday.