Libya NTC forces take most of Gaddafi stronghold Sirte
Libyan transitional government forces are battling pro-Gaddafi fighters in the centre of Sirte, one of the last cities loyal to the ousted leader.
Gun battles are taking place around the Ouagadougou conference centre where Gaddafi loyalists are holed up.
The BBC's Jonathan Head, in Sirte, says transitional government forces have largely taken the town but are meeting stiff resistance.
Thousands of civilians have left Sirte but many have remained behind.
Sustained tank and mortar fire has been targeting Sirte and huge columns of smoke are visible across the city, some 360km (225 miles) east of Tripoli, our correspondent says. Many buildings have been hit and are on fire.
This appears to be the final push for Col Muammar Gaddafi's home town, he adds, as the country has been unable to think about the future until Sirte falls.Two-pronged assault
At the scene
We're inside one of the housing estates that Col Gaddafi built for the people of Sirte. Early this morning we watched tanks and rockets being fired by government volunteer forces into this housing estate. It was a tremendous barrage. Now we're inside it.
The snipers who were here, firing back at that time, have been driven down almost towards to the coast, into much smaller pockets of Sirte.
These houses are completely full of holes. I can hear sporadic gunfire all around me as the government fighters try and go from house to house to find snipers who are there. There's a thick pall of black smoke from the burning buildings. It's been a dramatic day, a really big push for government forces.
Sirte is like a ghost city: there are very few people here now. The bombardment was so sustained this morning. This is a lost cause for them (pro-Gaddafi forces): it's the last significant piece of territory they hold, and yet they've continued to fight.
The fighters we've been going in with have taken significant casualties. The commander we stayed with last night was hit in the chest and died this morning.
Troops loyal to the National Transitional Council (NTC) are coming from both Misrata in the west and Benghazi in the east.
The Benghazi forces are only 1km (0.6 mile) from the city centre but have faced heavy resistance from snipers inside the city.
Our correspondent says pro-Gaddafi forces are firing from every house that they hold.
The Ouagadougou conference centre, where many of the Gaddafi loyalists are believed to have barricaded themselves in, has become the focus of the fighting.
There was sustained fire from mortars, machine guns and snipers around the centre, holding off NTC forces.
Ambulances have been bringing a steady stream of the wounded to a field hospital west of Sirte. At least 50 people have been injured, among them civilians as well as fighters.
The AFP news agency said at least nine bodies had been brought to the field hospital by early afternoon on Friday.
On Thursday, an NTC military commander Col Abdel Salam Gadallah said three quarters of the city was in their hands.
"God willing, in two days maximum, all of Sirte will be clean."
The NTC troops have given civilians in Sirte the opportunity to leave, but there are fears that thousands have been unable to do so or believed warnings by pro-Gaddafi fighters that they would be attacked by the interim forces if they surrendered.
Efforts to negotiate with loyalist commanders have also failed.
The attack on Sirte came just hours after Col Gaddafi urged Libyans to take to the streets "in their millions" to resist the interim leaders.
In a poor-quality audio message broadcast on Thursday on Syrian-based Arrai television, he said conditions in Libya had become "unbearable" and that the National Transitional Council (NTC) were not the country's legitimate leaders.
"I say to them, do not fear anyone. You are the people, you belong to this land," said Col Gaddafi, telling people to make their voices heard against the "Nato's collaborators" of the NTC.
The ousted leader's whereabouts remain unknown. Several of his family member are in hiding or have fled the country.