UK agencies, including the British Red Cross, Oxfam and ActionAid, are joining together to raise money for medical aid, emergency shelter, food and clean water.
Thousands of buildings have been destroyed in the disaster and responders have been searching the rubble for survivors. Many people have lost homes, leaving them without shelter in freezing, winter conditions, the DEC says.
The charities say access to clean water is going to be difficult in the coming days, and waterborne diseases will be a hazard.
DEC chief executive Saleh Saeed, on the other hand, described the scenes in Turkey and Syria as “heartbreaking”, with thousands “losing loved ones suddenly in the most shocking of ways”.