Rebels told the BBC they had advanced several miles eastward to near the next coastal town, Tawargha.
Casualties were flowing into a Misurata hospital, and residents were coming to give blood, they said. Moammar Gadhafi's forces were rocketing the rebels' western stronghold.
In Tripoli, the embattled dictator vowed a fight to death as NATO escalated its campaign with an unusual daytime raid that began Tuesday morning and went on past midnight, The New York Times reported.
Two acres of Gadhafi's Bab al-Aziziya compound, including several buildings, were leveled.
Amid the attack, Gadhafi went on state television and declared: "We welcome death. Martyrdom is a million times better."
"I am now speaking as planes and bombs fall around me," he said. "But my soul is in God's hand. We will not think about death or life. We will think about the call of duty."
A spokesman said at least 31 civilians were killed Tuesday by NATO bombing in Tripoli. The government said airstrikes Monday night targeted state television facilities, killing two.
A NATO diplomat told the Times: "There's a psychological aspect to the campaign, and we're sending a clear message: There is only one way out, and that is to go."