ANTAKYA, Turkey/JANDARIS, Syria: The rescue of several survivors from the rubble of buildings in Turkey lifted the spirits of weary search crews on Friday, four days after a major earthquake struck the country and neighbouring Syria, killing at least 20,000 people.

Cold, hunger and despair gripped hundreds of thousands of people left homeless by the tremors, the deadliest in the region for decades.

Several people were rescued from the rubble of buildings during the night, including a 10-year-old boy saved with his mother after 90 hours in the Samandag district of Hatay province.

Also in Hatay, a seven-year-old girl named Asya Donmez was rescued after 95 hours and taken to hospital, the state-owned Anadolu news agency reported.

But hopes were fading that many more would be found alive in the ruins of thousands of collapsed buildings in towns and cities across the region.

The death toll from the 7.8 magnitude earthquake and several powerful aftershocks across both countries has surpassed the more than 17,000 killed in 1999 when a similarly powerful earthquake hit northwest Turkey.

It now ranks as seventh most deadly natural disaster this century, ahead of Japan's 2011 tremor and tsunami and approaching the 31,000 killed by a quake in neighbouring Iran in 2003.

A Turkish official said the disaster posed "very serious difficulties" for the holding of an election scheduled for May 14 in which President Tayyip Erdogan has been expected to face his toughest challenge in two decades in power.

With anger simmering over delays in the delivery of aid and getting the rescue effort underway, the disaster is likely to play into the vote if it goes ahead.

The first U.N. convoy carrying aid to stricken Syrians crossed over the border from Turkey.

In Syria's Idlib province, Munira Mohammad, a mother of four who fled Aleppo after the quake, said: "It is all children here, and we need heating and supplies. Last night we couldn't sleep because it was so cold. It is very bad."

Hundreds of thousands of people in both countries have been left homeless in the middle of winter. Many people have set up crude shelters in supermarket car parks, mosques, roadsides or amid the ruins.

Survivors are often desperate for food, water and heat.

Some 40% of buildings in the Turkish city of Kahramanmaras, the epicentre of Monday's main quake, are damaged, according to a report by Turkey's Bogazici University.

ROADSIDE FIRES

At a petrol station near the Turkish town of Kemalpasa, people picked through cardboard boxes of donated clothes. In the port city of Iskenderun, Reuters journalists saw people huddled round fires on roadsides and in wrecked garages and warehouses.

Authorities say some 6,500 buildings in Turkey collapsed and countless more were damaged.

The death toll in Turkey rose to 17,674 by Thursday night, Vice President Fuat Oktay said. In Syria, already devastated by nearly 12 years of civil war, more than 3,300 people have died, according to the government and a rescue service in the rebel-held northwest.

In the devastated Syrian town of Jandaris, Ibrahim Khalil Menkaween walked in the rubble-strewn streets clutching a white body bag. He said he had lost seven members of his family, including his wife and two brothers.

"I'm holding this bag for when they bring out my brother, and my brother's young son, and both of their wives," he said. "The situation is very bad. And there is no aid."

Turkish officials say some 13.5 million people were affected in an area spanning roughly 450 km (280 miles) from Adana in the west to Diyarbakir in the east. In Syria, people were killed as far south as Hama, 250 km from the epicentre.

Rescue crews working in the dark and in freezing temperatures looked for survivors at a collapsed building in the city of Adiyaman, Turkish broadcasters showed.

Teams called for silence, asking all vehicles and generators to stop and reporters to keep quiet as they listened for any sound of life from the mangled concrete.

Many in Turkey have complained of a lack of equipment, expertise and support to rescue those trapped - sometimes even as they could hear cries for help.

Greece sent thousands of tents, beds and blankets and Israeli satellite intelligence was helping map the disaster zones in Turkey with technology predominantly used for special operations, the Israeli military said.

The World Bank is providing Turkey with $1.78 billion in relief and recovery financing, $780 million of which will become available immediately. The U.S. Agency for International Development will provide $85 million in urgent humanitarian assistance to Turkey and Syria.

SYRIA OVERWHELMED

In Syria, relief efforts are complicated by a conflict that has partitioned the country and wrecked its infrastructure.

The U.N. aid convoy entered Syria at the Bab Al Hawa crossing - a lifeline for accessing opposition-controlled areas where some 4 million people, many displaced by the war, were already relying on humanitarian aid.

U.N. Secretary-General Antonio Guterres pushed for more humanitarian access to Syria, saying he would be "very happy" if the United Nations could use more than one border crossing to deliver help.

The Syrian government views the delivery of aid to rebel-held areas from Turkey as a violation of its sovereignty and territorial integrity.

President Bashar al-Assad has chaired emergency meetings on the earthquake but has not addressed the country in a speech or news conference.