Rescuers in Turkey and Syria dug with their bare hands through the freezing night Tuesday hunting for survivors among the rubble of thousands of buildings felled in a series of violent earthquakes.

The confirmed death toll across the two countries has soared above 4,300 after a swarm of strong tremors near the Turkey-Syria border - the largest of which measured at a massive 7.8-magnitude.

Turkish and Syrian disaster response teams report more than 5,600 buildings have been flattened across several cities, including many multi-storey apartment blocks that were filled with sleeping residents when the first quake struck.

In the city of Kahramanmaras in southeastern Turkey, eyewitnesses struggled to comprehend the scale of the disaster.

Turkey’s relief agency AFAD on Tuesday said there were now 2,921 deaths in that country alone, bringing the confirmed tally to 4,365.

There are fears that toll will rise inexorably, with World Health Organization officials estimating up to 20,000 may have died.