Anti-Gaddafi fighters on Wednesday admitted heavy losses and hospitals full of wounded from their assault on the deposed despot's hometown, forcing them to send abroad critically hurt troops.

At least 45 National Transitional Council (NTC) fighters have been killed and more than 200 wounded -- mostly by explosions or gunfire -- since they launched an offensive against Sirte last week, medics in Misrata said.

"The offensive on Sirte has been high intensity in terms of casualties," Dr Suheib Abu Garza told AFP in Misrata, about 150 kilometres (95 miles) east of Sirte, where the casualties of battle are being brought.

Garza said he had not seen such volumes of serious cases since forces loyal to Moamer Gaddafi laid siege to Misrata soon after the rebellion began in February.

NTC fighters moved in on Sirte, one of Gaddafi's final strongholds, from the west and south on September 15, while another NTC force is still fighting its way towards the city from the east.

Gaddafi's forces have put up unexpectedly fierce resistance and the NTC fighters have been forced to retreat from the city by night to allow NATO warplanes to target their weaponry.

At least three NTC fighters, all in their 30s, were killed in Sirte and 17 others were wounded in fighting on Tuesday, Misrata's general hospital, which centralises casualty figures, reported.

Sporadic rocket fire and mortar exchanges shook Sirte, witnesses said, although the former rebels have reduced their use of heavy artillery since Sunday in a bid to give families a chance to flee.

Meanwhile, 16 patients -- most in critical condition -- were evacuated on a Qatari military plane to Malta, easing the pressure on overwhelmed hospitals.

"There's too much pressure in the operating rooms so we are sending those in critical condition to operating theatres abroad," Dr Mahmud al-Bakhush told AFP.

Four of Misrata's CT scan machines were inoperative on Tuesday, complicating the assessment of trauma patients while intensive care units were so overwhelmed doctors were battling to cope.

"We've almost run out of ventilators," said Dr. Hakim Zakri.

NTC forces suspect Gaddafi enjoys a broad base of support in Sirte.

"The majority of residents are with Gaddafi," said Zuber al-Gadir, spokesman of the Misrata military council, adding the loyalty stems from the fugitive leader's control over media.