Dozens of people were killed and many more were wounded in an air strike that destroyed a Syrian bakery where a large crowd of people was queuing for bread, activists said.
If confirmed, it would be one of the deadliest air strikes of Syria's civil war.
"There is no way to really know yet how many people were killed. When I got there, I could see piles of bodies all over the ground. There were women and children," said Samer al-Hamawi, an activist in the town of Halfaya. "There are also dozens of wounded people."
Rami Abdelrahman, of the Syrian Observatory for Human Rights, said the death toll was still 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, until we have more information."
Halfaya, in the central province of Hama, had been seized by rebels last week in a push to seize new territory in their 21-month-old revolt against President Bashar al-Assad.
Another activist said residents picking through the bodies were still determining which were wounded and which were dead.
Mr al-Hamawi, who spoke via Skype, uploaded a video of the scene that showed dozens of dust-coated bodies lined up near a pile of rubble beside a concrete building with blackened walls.
Screams could be heard in the video as some men rushed to the scene on motorcycles and other residents limped away. Dozens of dead bodies could be seen.
Activists said more than a thousand people had been lined up at the bakery in Halfaya.