"The tanks are everywhere in the city and are opening fire on houses. I saw at least seven speed outside my house and the shelling does not stop," one resident told AFP by telephone.

"Pray for us," the resident said before the call was abruptly cut.

A doctor also reached by telephone said: "I am caught under the fire. I cannot talk to you now."

The opposition website Al-Manara said 40 tanks rolled into Zawiyah and were attacking homes in the city, a key protest centre west of Tripoli where rebels and Qadhafi loyalists have been battling for hours.

Medics and witnesses earlier said at least seven people were killed and dozens wounded in an assault by Qadhafi forces.