A column of NTC troops thrust towards central Sirte from positions east along the Mediterranean coast, coming under heavy rocket and small arms fire as they inched forward house by house.
They advanced about a kilometre (1,000 yards) into the city centre from the south and east by the afternoon, backed by heavy shelling and tanks.
"The revolutionaries are less than one kilometre from the central square. We control about 90 percent of Sirte," said Makhluf el-Ferjani of the Sirte military council.
Little more than sniper fire was coming back at them, but at least 17 NTC fighters were killed and dozens more were wounded on Monday, medics told AFP.
"They have nothing left," said NTC fighter Khaled Abu Zakuk of Kadhafi loyalists.
"It's like slaughtering a chicken. Militarily, they are finished, but they are still moving," said another new regime fighter, Tarek Drissa.
Burned-out vehicles littered the streets as NTC tanks and artillery pounded Kadhafi positions in open ground in the Dollar area of Sirte from a ridge some four kilometres (two and a half miles) inland, which they seized on Sunday.
On the third day of what commanders have touted as a final assault, NTC troops captured Sirte's showpiece conference centre, university campus and hospital on Sunday, AFP correspondents said.
But the military gains came at a heavy price, with medics reporting 13 dead and 90 wounded on the western side of Sirte alone.
The bodies of another four NTC fighters were recovered from the city's Ibn Sina hospital following its capture from Kadhafi's forces.
The hospital's upper floors were blasted after a massive firefight broke out late on Sunday, with intense machinegun and rocket fire.
"It's chaotic," said Red Cross spokeswoman Dibeh Fakhr, as medics wheeled patients out on beds and shells rocked the area.
A convoy of nine vehicles, including four large trucks, waited outside to ferry the patients out of the war zone.
"This is not a functioning hospital. The patients need evacuation because the wards have all been hit. There were three doctors here last week, but yesterday there was just one."
The wounded were still on beds in the corridors, all of them men of fighting age whom the NTC fighters accuse of being Kadhafi's loyalists -- something they denied.
"They think I was with the Kadhafi fighters but it was just an accident," said Abdullah Mohammed Faraj, a 24-year-old with a stump for a right arm.
Beside him an NTC fighter said: "Tell the truth. Be a soldier. Be a man."
In Bani Walid, a desert oasis 170 kilometres (105 miles) southeast of Tripoli, the military said NTC fighters withdrew from forward positions in a "tactical pullback" after intense fighting on Sunday.
"We lost 17 fighters in fierce clashes on Sunday and our forces have withdrawn from the airport where they had taken control," said Salem Gheith, head of the NTC military command centre in the capital.
"We've received reinforcements from Tripoli and the Nafusa mountains, and we will resume the offensive," he said.
Regional NTC commander Yunes Mussa announced the airport's capture on Sunday, before the fightback by pro-Kadhafi forces.
The ferocity of the resistance in Sirte and Bani Walid has surprised Libya's new regime.
At least 70 NTC fighters have been killed and hundreds wounded since Friday when they launched a final push on Sirte after several days of NATO air strikes to soften up pro-Kadhafi positions.
NATO said its warplanes struck three armed vehicles in Bani Walid on Sunday, and its secretary general, Anders Fogh Rasmussen, said the alliance was close to terminating its mission in Libya.
"We are pretty close to the very end of this operation," Rasmussen said in Bucharest.
Rasmussen said despite the NTC's advances in Sirte, NATO "had no knowledge of the colonel's whereabouts," adding that Kadhafi "is not a target of our operation."
NTC commanders believe one of Kadhafi's sons, Mutassim, is in Sirte and that another, Seif al-Islam, once seen as the former strongman's successor, is hiding in Bani Walid, possibly with his father.
In a sign of growing diplomatic confidence, Libya's interim government said it recognises the Syrian National Council, a broad grouping of regime opponents officially assembled in Istanbul on October 2.
"The National Transitional Council has decided after a meeting today to recognise the Syrian National Council as the sole legitimate government in Syria," NTC member Mussa al-Koni told a news conference in Tripoli.