More than seven million children have been affected by the massive earthquake and a major aftershock that devastated Turkey and Syria last week, the United Nations said today, voicing fear that "many thousands" more had died.

"In Turkey, the total number of children living in the 10 provinces hit by the two earthquakes was 4.6 million children. In Syria, 2.5 million children are affected," James Elder, spokesman for the UN children's agency Unicef, told reporters in Geneva.

He spoke as rescue teams began winding down the search for survivors from the disastrous quake that has left more than 35,000 dead in the two countries.

"Unicef fears many thousands of children have been killed," Elder said, warning that "even without verified numbers, it is tragically clear that numbers will continue grow."

He said he feared the final toll would be "mind-boggling."

Given the catastrophic, and ever-increasing, death toll, he said it was obvious that "many, many children will have lost parents in these devastating earthquakes."

"It will be a terrifying figure," he warned.

Among the rubble, hundreds of thousands of homeless people face cold and hunger.

Families with children were "sleeping in the streets, malls, schools, mosques, bus stations and under bridges, staying with their children in open areas for fear of going home," he said.

"Tens of thousands of families are exposed to the elements at a time of year when temperatures are bitingly cold, and snow and freezing rain are common," he said, pointing to reports of rising numbers of children suffering from hypothermia and respiratory infections.