SIRTE - Libyan government forces fired rounds of heavy artillery at Muammar Gaddafi's home town of Sirte on Friday as they launched their largest assault so far to capture the last major bastion of support for the deposed leader.Taking the coastal town would be an important symbolic trophy for Libya's new rulers, and would bring them closer to finally gaining control of the whole country almost two months since their fighters seized the capital Tripoli.RELATED:Gaddafi warns developing world leaders of similar fate Humanitarian fears grow over Libya Sirte battle Forces loyal to the ruling National Transitional Council (NTC) are under pressure to intensify their advance but heavy resistance and gunfire by Gaddafi loyalists have prevented them from taking the city for weeks.Columns of black smoke rose above Sirte's skyline as NTC forces fired tank shells and rounds of artillery toward the city center from their positions to the east of Sirte.Thousands of civilians have fled Sirte as fighting intensified, describing an increasingly desperate humanitarian situation. Many were caught off guard by Friday's assault and fled in panic as explosions boomed around the city."There are strong strikes in all directions. Today we will finish it. God willing today we will capture Sirte," said Colonel Ahmed El-Obeidi, an NTC commander.NTC lorries with ammunition and artillery batteries were brought forward to the eastern front line, about 1.2 kilometres (0.8 miles) away from the city centre. Along with the desert town of Bani Walid, Sirte is one of the last strongholds still controlled by Gaddafi loyalists.Doctors at a field hospital east of Sirte said they heard a huge explosion inside the city after midnight. Colonel Obeidi said the explosion occurred after his forces hit a weapons storage facility belonging to Gaddafi supporters.Gaddafi loyalists who pulled back to Sirte when they lost control of other cities are putting up fierce resistance.They have been mainly using sniper fire and rocket-propelled grenades to prevent NTC forces from entering the city centre. The prolonged fighting has raised concerns about civilians in the coastal city of 75,000 people.At a field hospital several kilometers west of Sirte dozens of ambulances brought in at least 50 fighters and civilians wounded in the fighting. Most were seriously wounded.Medical workers tried to save an unresponsive woman. A child with a wounded leg sat on the floor. A helicopter landed near the hospital to carry some of the wounded to hospitals in Misrata, which lies west of Sirte.At a checkpoint near the field hospital, NTC fighters checked dozens of cars carrying families fleeing Sirte. "We didn't know there was going to be an assault," said Saeed Ramadan, whose vehicle had shrapnel holes and a broken window. "I couldn't sleep last night, there was very heavy shelling. I was afraid for my kids and had to get them out."A Sirte resident who gave his name as Abdel Nasser said: "Last night there was heavy random firing and shelling. We had a hundred narrow escapes. Conditions are tragic. You can smell the rotting corpses at the hospital."Concerns about the humanitarian crisis have focused on the Ibn Sina hospital in the city. Medical workers who fled Sirte say patients were dying on the operating table because there was no oxygen and no fuel for the hospital's generators.Hassan Briek, another fleeing resident, said fewer than half of Sirte's residents remained in the city and most had moved to three neighborhoods where there has been less fighting."There are lots of families in those districts of the city," Briek said. "No one knew there was going to be an assault today. No one is sleeping. Food isn't the problem. It's the shelling."Gaddafi and several of his sons are still at large more than seven weeks after rebel fighters stormed the capital and ended his 42-year rule.De facto Prime Minister Mahmoud Jibril said on Thursday that Gaddafi was hiding in southern Libya under the protection of tribes, crossing occasionally into Niger, and government forces expected to pinpoint his whereabouts soon.An audio recording of Gaddafi obtained by Reuters on Thursday from Syria-based Arrai television was the first sign of life from him since Sept. 20, when the same station last aired a speech by him."If the power of (international) fleets give legitimacy, then let the rulers in the Third World be ready," Gaddafi said in an apparent reference to NATO's support for NTC forces."To those who recognize this council, be ready for the creation of transitional councils imposed by the power of fleets to replace you one by one from now on."