Witnesses reported that there were 51 people wounded at one hospital - Badr hospital - alone.
They said the hospital was running short of blood for transfusions.
Tanks had surrounded another main hospital, al-Horani, one witness said.
A doctor who did not want to be named for fear of arrest said: "Tanks are attacking from four directions.
"They are firing their heavy machine guns randomly and overrunning makeshift road blocks erected by the inhabitants."
Another resident said snipers had climbed onto the roofs of the state-owned electricity company and the main prison.
President Bashar al Assad is attempting to crush an uprising against his 11-year rule that broke out in March/
The uprising was inspired by Arab Spring revolutions in Tunisia and Egypt, and has spread across the country.
Syrian authorities have expelled most independent journalists, making it difficult to verify reports of fighting.
The Syrian leadership blames "armed terrorist groups" for most killings during the revolt, saying that more than 500 soldiers and security personnel have been killed.
An activist group, Avaaz, said in a report last week that Syrian security forces had killed 1,634 people in the course of their crackdown.
At least 2,918 had disappeared while another 26,000 had been arrested, many of whom were beaten and tortured, Avaaz said. Source