At least seven children died when boats carrying migrants sank off Greece on Wednesday, as rescue workers battled to save more youngsters on the seashore in the latest desperate scenes in Europe’s refugee crisis.

At least seven children died when boats carrying migrants sank off Greece on Wednesday, as rescue workers battled to save more youngsters on the seashore in the latest desperate scenes in Europe's refugee crisis.

Three adults also died as four vessels went down on the dangerous sea crossing from Turkey and more than 200 people, many suffering hypothermia, were rescued from one sinking off the north coast of the Greek island of Lesbos.

Later in the evening, a drowned woman and the bodies of two children were found floating off the Greek island of Agathonisi, just a few kilometers from the Turkish coast.

A one-year-old baby remained in a critical condition Wednesday night, according to port police.

Port police said it was not clear how many people might be in the water, with survivors giving a confusing picture of the number of people who were on the boat that capsized off Lesbos.

The new accidents brought to 39 the number of migrants found dead in Greek waters this month.

"The priority for Europe must remain the secure resettlement of refugees arriving from their countries of origin," said Greek shipping minister Thodoris Dritsas in a statement.

"As long as European nations feed their national egos, smugglers will make enormous sums to the detriment of the lives of refugees," he added.

Amnesty International's Deputy Europe Director Gauri van Gulik said it was "obscene that European leaders allowed such a chain of tragedies on its shores".

Since the start of the year, 560,000 migrants and refugees have arrived in Greece by sea, out of over 700,000 who have reached Europe via the Mediterranean, according to the International Office for Migration (IOM).

More than 3,200 people have died during these crossings, most of them children, the IOM says.

Also Wednesday, Europe's maritime anti-people-smuggling mission, Operation Sophia, rescued about 1,000 migrants from six dinghies and a fishing boat off the Libyan coast, the Italian coastguard said.