An explosion of unknown origin at a weapons depot in the northwestern Syrian province of Idlib killed at least 39 people, including 12 children on Sunday, a war monitor said.
An AFP correspondent at the site in the rebel-held town of Sarmada near the Turkish border said the explosion caused two buildings to collapse.
On Sunday morning, rescue workers used a bulldozer to remove rubble and extract trapped people, the correspondent said.
Rami Abdel Rahman, head of the Syrian Observatory for Human Rights monitor, said the death toll could rise as dozens were still missing.
“The explosion occurred in a weapons depot in a residential building in Sarmada,” the head of the Britain based monitor said.
But the cause of the blast was “not yet clear”, Abdel Rahman added.
A rescue worker carried the motionless body of a small child from the wreckage to an ambulance, the AFP correspondent said.
Behind mounds of rubble, the facade of a building was scorched black, due to a fire after the blast.
A civil defense source told AFP that women and children were among the dead.
But rescue workers had pulled out “five people who were still alive”, the source said.
Most of Idlib is controlled by rebels and extremists led by Hayat Tahrir al-Sham, but ISIS also has sleeper cells in the area.
The regime holds a small slither of southeastern Idlib.
In recent months, a series of explosions and assassinations -- mainly targeting rebel officials and fighters -- have rocked the province.
While some attacks have been claimed by ISIS, most are the result of infighting since last year between various other groups.
In recent days, regime forces have ramped up their deadly bombardment of southern Idlib and sent reinforcements to nearby areas they control.
President Bashar al-Assad has warned that government forces intend to retake Idlib, after his Russia-backed regime regained control of swathes of rebel held territory elsewhere.
Around 2.5 million people live in the province, half of them displaced by fighting in other parts of the country.
More than 350,000 people have been killed and millions displaced since Syria’s civil war started in 2011 with the brutal repression of anti-government protests.