At least 48 people were killed when a tanker bomb ripped through the centre of a rebel-held Syrian city along the Turkish border, damaging buildings and leaving rescue workers searching for survivors amid the wreckage.

The explosion went off early on Saturday afternoon outside a local court house and security headquarters operated by the opposition fighters who control the town.

“It hit the busiest part of the town,” resident and activist Saif Alnajdi said.

The scene of a bombing in the rebel-held Syrian city of Azaz, near the Turkish border, on 7 January (AP)

Azaz, only a couple of miles away from the Turkish border, is a hub for anti-government activists and opposition fighters, as well as many displaced from the recent fighting in Aleppo.

Activists say its pre-war population of 30,000 has swelled. It is also sandwiched between rival groups, including Kurdish fighters to the west and Turkey-backed opposition groups to the east. Isis militants have been pushed back farther east by the Turkey-backed fighters.

No one has yet claimed responsibility for the attack, although Isis has been accused of carrying out attacks there before and was suspected of being behind Saturday's bombing as it continues to battle rebels based in the city.

Footage of the aftermath of the explosion showed a gutted area. Activists shared photos of bodies lying in the street as large clouds of black smoke lingered overhead.

Rami Abdurrahman, the head of the UK-based Syrian Observatory for Human Rights, said those killed included six opposition fighters. He said the explosion was caused by a rigged water or fuel tanker, which explains the large blast and high death toll.

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The activist-operated local Azaz Media Centre put the death toll at 60, adding that search and rescue operations continued for hours after the explosion. The Observatory said the explosion took place near the local courthouse operated by rebel groups.

Mr Alnajdi said rescue workers were still working to identify those killed and ensure bodies were removed from the area, suggesting that the death toll was not final.

He said some of the severely wounded were transported across the border into the Turkish town of Kilis for treatment. The Turkish state-run Anadolu news agency said 53 wounded Syrians were brought to Kilis’ local hospital for treatment, including five in critical condition, transferred to Gaziantep. The agency said one later died.

Mr Alnajdi said some witnesses saw the vehicle – which he described as a tanker – drive into the town's centre.

Residents of Syria’s Azaz caught in the crossfire

The court house and the security headquarters were damaged, as well as the Red Crescent and municipality offices, according to activists in the area.

Media activist Bahaa al-Halabi said witnesses reported many unidentified bodies because of the strength of the explosion. Footage shared online showed a large plume of black smoke rising above the chaotic street and the sound of gunfire in the background as onlookers gathered around the site. In one instance, a father ran away from the scene, carrying his child to safety.

Many rebels and civilians who were pushed out of Aleppo city during a massive government offensive late last year have resettled in Azaz. Syrian Kurdish forces control territory to the west of Azaz, and have often tried advancing toward the town, causing friction with Turkish troops and allied Syrian opposition fighters. To the east, opposition fighters backed by Turkey have been pushing back Isis extremists, gaining territory and advancing on the Isis stronghold of al-Bab, further east. Turkey considers Syria Kurdish factions there terrorists, linked to a local group it is battling at home.

A nationwide cease-fire has gone into effect across most of Syria after Russia and Turkey, who support opposite sides of the conflict, reached an agreement late December. It is set to pave the way for peace talks between Assad’s government and the opposition in Kazakhstan later this month. Isis group and al-Qaeda-linked group Jabhat Fateh al-Sham are not included in the deal, according to the Syrian government.