The Revolution Leadership Council of Hama told Reuters that the massacre began early on Thursday morning, when government troops and pro-regime militia forces surrounded the town of Tremseh, before firing on its inhabitants with tanks and helicopter gunships.
Once the shelling was over, the militiamen reportedly began killing civilians 'execution-style' with guns and knives, and burning down homes.
Rami Abo Adnan, a Hama resident who witnessed the slaughter, told Sky News that most of the victims "were slaughtered by knife, including women and children. Burning bodies were found."
Fadi Sameh, an anti-regime activist, was quoted by Reuters as saying: "Whole houses have been destroyed and burned from the shelling. Every family in the town seems to have members killed. We have names of men, women and children from countless families."
On Thursday afternoon, the activist claimed that around 150 bodies had been piled in the town mosque, and dozens more were thought to be trapped under the debris of burnt and destroyed houses. The death tool is likely to rise further as and when these corpses are recovered.
If the early reports are accurate, the Tremseh massacre would be the worst atrocity yet committed during the struggle between president Bashar al-Assad and his opponents, which began in March 2011.
Syrian state television, which is controlled by the Assad government, claimed that national security forces had clashed with "terrorist" groups, following a plea for assistance from local residents. According to a report by the Syrian Arab News Agency, "The terorists ransacked, destroyed and burned scores of village houses, before the competent authorities arrived."
The report added that foreign news agencies were trying to "manipulate public opinion" by blaming the attack on government forces, and talked of international "phobia from the foiling of the conspiracy against Syria by some Zionist media channels."
The bloodshed comes at a time when UN Security Council members are pushing for more sanctions on the regime, but this is being opposed by Syria's key ally, Russia.