Syrian rebels have shelled a government-held neighbourhood in the northern city of Aleppo, killing at least nine people and wounding dozens, Syrian state television and an activist group have reported.

Footage aired on Syrian state television on Saturday showed damaged buildings and injured people being treated at the overcrowded local hospital.

State TV said the shelling on the predominantly Christian and Armenian neighbourhood of Sulaymaniyah in Aleppo killed nine people, wounded another 50 and damaged several buildings. It said dozens of people were still trapped under rubble.

The Britain-based Syrian Observatory for Human Rights, which has a network of activists around the country, however, said the shelling killed 27 people and wounded many more.

Hours after the shelling, helicopter gunships struck a market in Aleppo's rebel-held neighbourhood of Maadi in an apparent retaliation by the Syrian government, according to the observatory and the opposition-run Aleppo Media Centre.

The observatory said the airstrike killed ten people and wounded dozens, some seriously.

The Aleppo Media Centre reported casualties but did not provide a precise toll.

The violence came as the head of the UN agency for Palestinian refugees planned to undertake an "urgent mission" to Damascus on Saturday amid concerns over the humanitarian crisis in the Palestinian camp of Yarmouk, most of which has been captured by the Islamic State of Iraq and the Levant [ISIL].

Pierre Krahenbuhl, who heads the UN agency for Palestinian refugees UNRWA, will discuss the situation in Yarmouk and meet with displaced refugees.

The visit is "prompted by UNRWA's deepening concerns for the safety and protection of some 18,000 Palestinian and Syrian civilians, including 3,500 children" who remain in the Yarmouk camp, the agency said in a statement.

"Yarmouk remains under the control of armed groups, and civilian lives continue to be threatened by the effects of the armed conflict in the area," it said.

On April 1, ISIL launched an assault on the Palestinian armed group Bait al-Maqdis, which is one of numerous factions that share control of the district.

After the government claimed that ISIL took over most of the camp - which has been denied by local activists - regime forces stepped up their shelling of the district, further worsening the area's humanitarian crisis.

The Syrian Observatory for Human Rights, a monitoring group, reported on Thursday that since April 4, government helicopters have dropped 36 barrel bombs, which are highly indiscrimate and destructive explosives, on Yarmouk.

Krahenbuhl, who will meet displaced refugees on Sunday in a school near the camp, will discuss "with the government of Syria... peaceful approaches to addressing the humanitarian consequences of the situation in Yarmouk".

He will also meet with deputy special envoy Ramzy Ezzeldin Ramzy, who was sent by UN chief Ban Ki-moon on Friday to Damascus.

Since 2012, Yarmouk has seen ongoing clashes between regime forces and Syrian rebels, with Palestinian factions divided and fighting on both sides.

The sprawling district, once home to 160,000 Palestinians as well as Syrians, has endured an army siege since 2013.