Rebels, backed by NATO helicopters, have tried for the past three weeks to seize this vital port 240 kilometres (140 miles) southwest of their eastern stronghold Benghazi.
On Wednesday, they were poised on the eastern fringes of the city, the outskirts of its residential area, an AFP journalist saw.
By today, after a day of fighting, the rebels said they had taken control of "residential zone number three," one of the three in Brega.
"Every day, we are gaining ground. We are at the entrance of the city. Some of our fighters have even got inside the residential area," said Fawzi Bukatif, a civil engineer who became a top commander of the insurrection.
"We could be inside the city today, but with heavy casualties. We are trying to spare lives. It's wiser to go slowly, to secure methodically our advance," Bukatif, who is in charge of operations in Brega, told AFP.
His operation room is in a lack-lustre seaside building surrounded by containers near Zuwaytina, 70 kilometres (43 miles) northeast of Brega.
"Who holds Brega controls the centre part of the country and its oil fields," he said.
In Brega, the transparent waters of the Mediterranean meet the desert of Syrte, a vast natural frontier driving a wedge between the Tripolitan west and the Cyrenic east of the north African nation.
Brega itself stretches several dozens of kilometres from east to west along the coastal road linking the rebel-held eastern city of Ajdabiya and the key oil hub of Ras Lanuf, controlled by forces loyal to strongman Muammar Gaddafi.
The oil town springs forth from the sands complete with a refinery, a port, a residential area and industrial complexes.
Rebels determined to take it have embarked on a three-pronged attack straddling the coast, the road from Ajdabiya and the south.
"We are surrounding the city. We have been using our artillery to empty the city," Bukatif added.
In turn, Gaddafi's troops have formed solid defence lines.
They have planted hundreds of mines in a bid to block the rebel advance, hidden their arms depots in warehouses and maximised an ingenious network of underground tunnels to move their tanks and vehicles undetected by NATO.