He has ruled Libya for 42 years, but Muammar Gaddafi's defiant regime was on Sunday entering its final hours as rebel fighters entered the capital, Tripoli.

In another day of dramatic advances, opposition fighters pushed forward from the western town of Zawiya along the coastal highway to Tripoli. From the frontline in the village of Maya, the chimneys of Tripoli's power station could be seen shimmering in the distance. The regime's last moments were being played out in a green landscape of orange groves, olive trees and seaside restaurants.

Ahmad Gaid, a 25-year-old fighter, gave his verdict on government troops, who on Sunday retreated to, and then further beyond, the "27 bridge" – 17 miles (27km) from the centre of Tripoli. "They are becoming weak. They are very frightened," he said.

Gaid had taken temporary shelter together with medical staff in a roadside house. Up ahead was an enemy sniper. Bullets whined past. A rebel pickup truck responded with 12.5 anti-aircraft artillery: an unmistakable, thunderous boom-boom-boom-boom.

The fighters had sent in their one tank, which promptly broke down. "There was something wrong with its chamber," Mohamad, a 25-year-old Libyan-American volunteer, said calmly.

Rebel vehicles streamed to and from the battle. Some fighters were in a hypnotic daze. One staggered into the shelter and recounted how his vehicle veered off the road after its tyre was shot at. A bullet hit one of his comrades in the face. "What happened to him?" he inquired. "He died," Mohamad replied.

He said he was hoping to rescue his US-educated father and brother, both rounded up by the regime and now in jail in Tripoli.

The rebels may lack heavy weapons, but they have one supreme advantage: allied airpower. On the road from Zawiya to Maya, an air strike had flattened a Turkish restaurant used by Gaddafi's troops as a command point. The building was a skeletal ruin, the restaurant's sandbagged entrance blown out.

Nearby, opposition militiamen were combing through a dense forest of cypresses. Behind them was the town of Zawiya, definitively seized by the rebels on Saturday following a week-long battle, and now a ruined mess.

Two plastic mannequins lay surreally in one street; most of the buildings in the central square had been destroyed. The city was peaceful on Sunday.

The drama of Libya's six-month revolution has now shifted to further along the coast, where the final act awaits. On the southern road to Tripoli, volunteers from the Tripoli brigade massed near the government-held town of Aziziya, 25 miles south of Tripoli. They were camped out at a primary school awaiting orders. Up ahead, Nato jets were pounding the sites from where Gaddafi's troops had been imprudently launching Grad missiles.

"We will win this war," Mohammed, a 24-year-old law student, declared. Why? "Because we believe in God. God and then Nato," he replied. His faith wasn't misplaced: every few minutes there was a loud, percussive, earth-shaking rumble, as Nato jets pulverised the way ahead. After each strike, the fighters broke into chants of "Allahu Akbar".

"Morale is very high. The rebels are controlling most of Tripoli," he said.

On Saturday, a Libyan opposition TV channel claimed Gaddafi and two of his sons had fled the country. It offered no proof and the regime flatly denied the report. But it triggered a pre-planned and well co-ordinated uprising in several parts of the capital, as well as celebrations in rebel-held Benghazi, Misrata, and Zintan, the opposition stronghold in Libya's western mountains.

Issam Mohmed Shebani, the son of a prominent Libyan exile, said at least 133 civilians had been killed in Tripoli's fierce fighting, citing opposition sources.

Other fighters preparing to launch the final assault on Tripoli said Gaddafi's desperate soldiers were firing mortars into residential areas. Nabil Nassar left London two months ago to join the anti-Gaddafi war. He said he had spoken to his family bunkered down in Tripoli. "There is non-stop fighting since dawn. Most families have got some weapons. They are also managing to get ammunition. But government troops are firing on them from the top of the mobile network tower," he said. Nassar added that he lived in Britain and has an MA in diplomatic relations. He left the UK, he said, having tired of political tactics. "I got bored of taking part in protests," he said.

According to his relatives, opposition areas inside Tripoli had set up committees to protect residential areas and were manning their own checkpoints.

Behind the frontline, there was a mood of triumph and certainty that the overthrow of Libya's hated dictator was close. Families driving past checkpoints hooted and waved V-signs; rebels responded by cracking off celebratory shots.

On a roadside skip, someone had hung a stuffed effigy of Gaddafi. They had used a lot of white wool to improvise the leader's unruly hairdo. A petrol station had reopened, prompting long queues; a stall had set up business selling seasonal coriander and fennel. And what of Gaddafi himself? The fighters made clear on Sunday what would happen to him when – and if – they got hold of him. "We will kill him very slowly," one said.