The northern mountains are the only part of Latakia province, on Syria's Mediterranean coast, that are no firmly in the hands of the government.
Thirteen civilians were among those killed in the blast, the cause of which was not immediately clear, according to the Syrian Observatory for Human Rights.
On Friday, jihadist groups attacked government forces in the northwest of Hama province near the planned buffer zone.
The attack on a position held by the Jaish al-Izza rebel group took place on the edge of the northwestern province of Idlib, in an area due to be de-militarised.
The evacuation began with ambulances ferrying out the sick, the Syrian Observatory for Human Rights war monitor reported.
After four days of reduced bombardment, the intense air strikes had resumed on Wednesday following the collapse of talks between insurgent groups and Russian officers.
The Syrian Observatory for Human Rights says it’s made the gains since starting a ground offensive there a week ago.
The Britain-based Syrian Observatory for Human Rights said it was the highest 48-hour death toll in the Syria conflict since a 2013 chemical attack on eastern Ghouta.
Air strikes, rocket fire and shelling on the besieged suburbs of Damascus also wounded another 325 people, the Syrian Observatory for Human Rights said.
Iran-backed militias sowed “terrorism and sectarian strife” between Sunni and Shi‘ite Muslims, the communique said.
There was no comment from the Syrian army on the report that Qaryatayn, 120 km northeast of Damascus, had fallen.
The Syrian Observatory for Human Rights says at least 42 people were killed, identifying them as prisoners of Islamic State.
The Syrian Observatory for Human Rights and a doctor said air strikes near the town of Latamneh, northwest of Hama, had led several people to choke, saying it was a sign of a gas attack.
The ceasefire marks the biggest bet yet by Washington that it can work with Moscow to end the war.
Mohammad Darra Jamo was killed by gunmen at his home.
The 11 Western and Arab countries reached an agreement to send military support to aid Syrian rebels.
Western officials will meet the commander of the rebel force to discuss new aid.
Syrian troops forced rebels to abandon a battered Damascus suburb on Friday.
