A rocket killed two children on Saturday as their family joined the quickening exodus of civilians fleeing the battle for Muammar Gaddafi's hometown of Sirte, a Libyan medic said.
Some of the hundreds of people escaping the city said there had been civilian casualties in the city when residential buildings were hit by artillery fire by besieging new regime forces or NATO air strikes.
National Transitional Council (NTC) forces besieged the Ouagadougou Conference Centre on Saturday, a showpiece venue in Sirte where Gaddafi hosted the launch of the African Union.
A large force of some 100 vehicles, including anti-tank guns and multiple missile launchers, entered the city from the south at around midday (1000 GMT) and surrounded the compound.
"We are surrounding the Ouagadougou Centre," fighter Osama Blao told AFP as he returned from the front line.
A senior NTC commander said growing numbers of Gaddafi loyalists were also trying to get out of the city as their supplies of food and munitions dwindled.
The coast road west to Libya's third-largest city of Misrata was clogged with convoys of fleeing civilians, an AFP correspondent reported.
The two children killed "were torn to pieces," said Dr Ahmed Abu Oud, a field medic on the western side of Sirte. "They collected the body parts in bags."
Redwan Abdulrahim, whose small truck was piled high with suitcases and other possessions, said the situation in Sirte was increasingly difficult.
"It was really bad. We didn't know where the bullets and rockets were coming from," he said.
Hassan Duha, a commander in the Misrata military council operations room, said a growing number of Gaddafi troops were trying to hide among the escaping civilians.
"They throw away their IDs and they try to come out with the families," he said.
"We hear them on the radio saying they don't have electricity and they are running out of food and ammunition."
An AFP correspondent saw one Gaddafi officer surrendering on Saturday.
Major Mohammed Usba Hanish told his NTC captors that although he came from Gaddafi's birthplace in the small town of Qasr Abu Hadi, 20 kilometres (12 miles) south of Sirte, he had not been fighting as he was on sick leave.
"I am not involved. If I was involved, I would not be here," he said.
Hanish said that troops still loyal to the toppled dictator were facing growing shortages.
"The Gaddafi people are eating just bread. They are running out of food and ammunition."
At midday (1000 GMT) NTC forces opened an artillery barrage from the east on administrative buildings in the city centre.
"We are targeting buildings where Gaddafi's men are holed up. Our scouting teams have informed us that a lot of mercenaries are still in there and we are striking them too," said Colonel Hussein Idris as he supervised the barrage.
An AFP correspondent saw young NTC fighters open up with six Russian-built 130 mm cannons in the desert, firing dozens of shells in an hour.
Idris said most civilians have now fled the city as they had "time to leave in the past two days."
"There are some civilians still left, but most of them inside the city now are Gaddafi loyalists," he told AFP.
Dozens of Pakistani migrant workers were among the hundreds of Sirte residents fleeing to the east.
"NATO struck one big building, Imarat Tamim, two days ago, with 12 or 13 bombs," said Ashiq Hussein, who fled the city with 11 family members, including six children.
"The whole building with nearly 600 flats is razed to the ground now."
Hussein, an electrician originally from Lahore, worked in construction with a Libyan builder and has been in Sirte for 30 years.
"Two of my neighbours died yesterday in a NATO bomb which hit their home," he said as his family fled in two cars packed with essentials including mattresses, bags of rice and clothing.
Asked why NATO was hitting civilian buildings, Hussein said: "Maybe they have information that on rooftops there were Gaddafi men... But a lot of civilian buildings were getting hit.
"Also the incoming shells from NTC forces were hitting civilian homes. They are missing their targets and often hit civilian homes."
Mohammed, a Libyan, also said civilians were being caught in the shelling.
"My home was struck yesterday so I decided to leave early today with my family. I don't know whether it was a NATO bomb or one fired by rebels," he said.