An explosion at a weapons depot that toppled buildings in a rebel-held city in northwest Syria killed at least 39 civilians, including a dozen children, a monitor said.
An AFP correspondent at the Sarmada site in Idlib province, near the border with Turkey, said the explosion of unknown origin caused the collapse of two buildings.
Rescuers used bulldozers to remove debris and pull people trapped from crushed buildings, the correspondent said.
A source of civil defense told AFP that the rescuers had removed "five people who were still alive."
But the death toll rose as more bodies were recovered from the rubble, according to Rami Abdel Rahman, head of the monitoring group of the Syrian Observatory for Human Rights.
Three members of Hayat Tahrir al-Sham (HTS) also died, in addition to the 39 civilians, he said.
"The explosion happened in a weapons warehouse in a residential building in Sarmada," said the head of the monitor based in Britain, which depends on a network of sources inside Syria.
But the cause of the explosion "is not yet clear," Abdel Rahman added.
He said most of those killed were members of the family of HTS fighters, an alliance led by jihadists of the former al Qaeda affiliate who had been displaced to the area from the central province of Homs.
A rescue worker brought the immobile body of a small child from the remains to an ambulance, the AFP correspondent said.
The rescue workers of the Casco Blanco tried to lift part of a floor of one of the buildings with a tall crane, while three young people watched in silence, perched on a rock.
Behind the mounds of rubble, the facade of a building was scorched, due to a fire after the explosion.
Most of Idlib is controlled by rebels and HTS, but the Islamic State jihadist group also has dormant cells in the area.
The regime has a small slip southeast of Idlib.
In recent months, a series of explosions and assassinations – mainly against rebel officers and fighters – have shaken the province.
While some attacks have been claimed by IS, most are the result of infighting since last year among other groups.
The regime's forces since last week intensified their deadly bombing of southern Idlib and sent reinforcements to the nearby areas they control.
On Friday, 12 civilians, three of them children, were killed in the bombing of the regime of the cities of Khan Sheikhun and Al-Tah.
President Bashar al-Assad has warned that government forces are trying to retake Idlib, after his Russian-backed regime regained control of strips of territory controlled by rebels in other parts of Syria.
On Thursday, government helicopters dropped leaflets on cities in east Idlib, urging people to surrender.
The United Nations appealed on the same day to the talks to avoid "a civil bloodbath" in the province.
Jan Egeland, head of the UN humanitarian team for Syria, said: "The war can not be allowed to go to Idlib."
About 2.5 million people live in the province, half of them displaced by fighting in other regions of the country.
More than 350,000 people have died and millions have been displaced since the civil war in Syria began in 2011 with the brutal repression of anti-government protests.