At least 27 people have been killed and over 235 injured in hours of clashes between militia, police and armed residents in the Libyan capital, Tripoli.

The ministry of health called on people to donate blood as the injured arrived at hospitals.

This is the third outbreak of street fighting in ten days .

It underscores Libya's struggle to contain regional militias that helped overthrow Muammar Gaddafi two years ago but kept their guns. 

The violence began today when militia opened fire into a crow of protesters, who were demanding their removal from the city.

Protesters at first fled but then returned heavily armed to storm buildings where the militia - from the central coastal town of Misrata - were holed up.

Dozens of soldiers in army trucks arrived to try to separate the sides in the compound and sealed off roads to prevent more armed people joining the unrest.

Heavy smoke could be seen rising from the scene.
Air force planes circled overhead to monitor Tripoli's main roads.

"We want to make sure the militia don't bring in any reinforcements," a military spokesman said