The death toll from the earthquakes that struck Turkey and Syria earlier this week rose to more than 15,800 on Thursday, as rescuers scrambled for survivors trapped beneath the rubble in freezing winter conditions.

Turkish state news agency Anadolu Agency, citing the country's disaster management bureau, reported on Thursday that 12,873 people have died in Turkey alone from the quake.

Syria's health ministry, meanwhile, has calculated the death toll in government-controlled areas in the country at more than 1,200. The White Helmets responders group based in Syria's rebel-held region in the northwest said at least 1,600 people had died.

The Turkish government admitted on Wednesday that the country's disaster response could have been better.

Access to Twitter in the country — throttled following a flurry of online criticism of authorities — was restored early on Thursday after talks between the company and Turkish officials.

Summary of Turkey-Syria earthquake events on Wednesday

Turkey's Foreign Minister Mevlut Cavusoglu said his country is working to open two additional border gates to Syria to enable humanitarian aid into the war-torn country.

European Commission President Ursula von der Leyen said a donor conference for international aid for Syria and Turkey in the wake of Monday's devastating earthquake has been planned for March.

For the first time in 24 years, the Istanbul stock exchange announced that it is closing for five days in response to the earthquake.

Turkish President Recep Tayyip Erdogan, who visited the disaster area, acknowledged "shortcomings" in his country's response to the huge earthquake.

The sanctions-hit Syrian government has put in an official request to the EU for emergency assistance through the civil protection mechanism, the bloc's commissioner for crisis management has said.