At least 41 Syrian children aged under 12 have been killed in a double bombing by a lone assailant at a school in the government-controlled city of Homs, a monitor said.

They were among 48 people who died in the attacks in the Akrameh neighbourhood, the Syrian Observatory for Human Rights said, updating an earlier toll.

"At least 41 schoolchildren were killed in the double bombing at the Akrameh al-Makhzumi school in Homs city today. Several children are still missing, and the toll may rise further still," Observatory director Rami Abdel Rahman said.

The adults killed were four civilians and three members of the security forces.

One attacker carried out both bombings.

"He planted a bomb at one location at the school, and then blew himself up at another spot nearby," Abdel Rahman said.

Pro-regime Facebook pages posted pictures of the aftermath, including one of a pile of schoolbags abandoned on a pavement.

One page, named the Homs Youth Club, posted a video apparently shot at the scene, showing panicked residents rushing to evacuate children wearing blue and pink uniforms.

Some children shown in the amateur footage were yelling, and one boy being carried was visibly wounded.

Body parts and rubble could be seen in the footage, as well as a thick cloud of black smoke and a burning car.

There was no immediate claim of responsibility for the attack.

Al Qaeda group linked to similar bombings

Al Qaeda's branch in Syria, Al-Nusra Front, said it was behind a similar twin bombing in the central city that killed at least 12 people in May.

Homs governor Talal al-Barazi gave a toll of 31 killed and 74 wounded in Wednesday's attacks.

The children were between six and nine years old, he added.

The toll is among the highest suffered by children in suicide attacks in Syria since the conflict erupted more than three years ago.

In August 2013, a chemical attack on rebel-held areas in the outskirts of Damascus killed dozens of children, and the year before 49 children were killed in the Houla "massacre" in Homs province.

The Akrameh neighbourhood of Homs is home to a majority of Alawites, members of the same offshoot of Shiite Islam to which president Bashar al-Assad belongs.

The district has been targeted before, including on June 19, when at least six people were killed in a car bombing.

Homs was once dubbed "the capital of the revolution" against Assad.

Most of the city, except the battered Waar district, has returned to regime control after two years of bombardment and siege.

AFP