The death toll across both countries has now surpassed the more than 17,000 killed in 1999 when a similarly powerful quake hit northwest Turkey.
Hundreds of thousands of people across both countries have been left homeless in the middle of winter. Many have camped out in makeshift shelters in supermarket car parks, mosques, roadsides or amid the ruins, often desperate for food, water and heat.
Authorities say some 6,500 buildings in Turkey collapsed and countless more were damaged.
The death toll in Turkey rose to 17,674, Health Minister Fahrettin Koca said. In Syria, already devastated by nearly 12 years of civil war, more than 3,370 people have died, according to the government and rescue service in the rebel-held northwest.
At least 78,124 people were injured across both countries, according to authorities.
In the Turkish town of Iskenderun, streets were flooded as a result of the tremors, as tractors were deployed to help clear the streets from thick residues of mud.
Ukrainian rescue teams searched through the debris of residential buildings in Hatay with the aid of sniffer dogs. Kyiv has sent 88 people to Turkey to help with the disaster. The team includes specialists in search and rescue operations, doctors, dog handlers and firefighters.
The German army unloaded relief goods for Turkish earthquake victims at Incirlik Air Base after being rerouted from Gaziantep.
According to the German army, three Airbus A400M transport planes carried tents, cots and electric heaters.
Incirlik air base, which hosts US nuclear warheads, is located some 220 km (136 miles) by road west of Gaziantep.
Greece sent thousands of tents, beds and blankets on Thursday to help those left homeless by the quake, in an act of solidarity with a neighbour that is a Nato ally but also a historic foe.
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.
After facing criticism over the initial response, Erdogan said on a visit to the area on Wednesday that operations were now working normally and promised no one would be left homeless.
Reuters