A baby has been pulled alive from the rubble of one of several barrel bomb attacks carried out in Syria since Wednesday morning.

Government forces were behind the attacks in which the barrel bombs - "homemade" containers packed with explosives - were used in northern Syria, according to monitoring group the Syrian Observatory for Human Rights.

They occurred as Islamic State jihadists were closing in on the provincial capital Hasakeh, the group said.

Three separate fatal bombings were reported in Aleppo province in the north and Idlib province in the northwest on Wednesday.

Eighteen people were killed, including eight children, were killed in Tal Rifaat in Aleppo, when government helicopters dropped at least four of the devices, the Britain-based monitor said.

Two children were among 11 civilians who died when a barrel bomb exploded in the rebel-held eastern neighbourhood of Jubb al-Qubbeh in Aleppo city.

Eight members of one family died in an attack in the town of Kafr Sijna in Idlib province, the group said.

The Observatory, which relies on a network of sources on the ground, said the casualties were expected to rise because of the number of people seriously wounded.

On Thursday, the Observatory said 14 people - including seven children - died in barrel bombings in the villages of Hayyan and Deir Jamal, both north of Aleppo.

Barrel bombs have often fallen on schools, hospitals and markets in Syria and human rights groups are heavily critical of them, saying they kill a disproportionate number of civilians.

Syrian President Bashar al Assad has denied his troops use the bombs but evidence has been collected of the barrels being pushed out of helicopters.

Chemicals

Human Rights Watch has also said there is "strong evidence" the regime has dropped barrel bombs containing toxic chemicals on northern Syria.

The New York-based group said on Wednesday it had led an investigation into three attacks in Idlib province, which killed two people and affected 127 others, and that deadly chlorine was probably used in some, if not all of them.

"The Syrian government has used barrel bombs with toxic chemicals for more than a year while the (UN) Security Council has failed to act," said HRW's Philippe Bolopion.

Meanwhile, IS is continuing its assault on Hasakeh, the Observatory reported, detonating at least five car bombs as it advanced towards the city.

"(The clashes) ended with IS seizing all of the military checkpoints south of the city," the group said.

The capture of Hasakeh would give the group control of its second provincial capital after their capture of Raqqa last year.

More than 220,000 people have been killed in Syria since the conflict began in March 2011 with anti-government demonstrations that were met with a regime crackdown.