Dozens of people have been killed and many more wounded in an air strike that hit a Syrian bakery where a large crowd was queuing for bread, activists say.

If confirmed, the attack in the town of Halfaya will be one of the deadliest air strikes of Syria's 21-month civil war.

"I could see piles of bodies all over the ground. There were women and children," said activist Samer al Hamawi. "There are also dozens of wounded people."

Rami Abdelrahman, of the Syrian Observatory for Human Rights, said the death toll was still very unclear: "From looking at the videos, I expect the death toll to be around or above 50, and not higher than 100. But for now I am keeping my estimate at dozens killed."

Halfaya, in the central province of Hama, was seized by rebels last week.

Mr Hamawi, who spoke via Skype, uploaded a video of the scene showing dozens of dust-coated bodies near a pile of rubble beside a building with blackened walls. Screams could be heard as men rushed to the scene on motorcycles and people limped away.

It is claimed more than a thousand people were at the bakery.

It is believed more than 44,000 people have died since the eruption of protests against President Bashar al Assad, inspired by the Arab Spring revolutions in Tunisia, Egypt and elsewhere.