An international aid ship helping to evacuate people from the besieged Libyan port of Misrata has come under rocket attack from government forces.
Witnesses said at least five people died and there was widespread panic among those trying to board the ferry, the Red Star One.
Amid the chaos about 200 people were left behind when the ship sailed for Benghazi, rebel sources said.
The forces of Col Gaddafi have been pounding Misrata for several weeks.
In that time the port has become a lifeline, allowing in vital supplies and evacuating wounded people and migrant workers fleeing the fighting.
The Red Star One, chartered by the International Organisation for Migration (IOM), had to wait offshore for several days because of the continuing fighting.
It arrived in Misrata on Wednesday carrying 180 tonnes of supplies.
IOM official Othman Belbeisi said rockets started falling just minutes after he and others disembarked.
"The whole place was shaking and people started running in different directions," he said.
Witnesses said that, when panicking evacuees threatened to swamp the ship, the captain raised the gangplank and pulled away from the dock, separating some families.
But the ship briefly returned a few minutes later when a wounded patient's condition worsened. There were further chaotic scenes before the ship finally left for Benghazi.
Gemal Salem, a rebel spokesman, told Reuters: "The bombing has caused so many casualties among Libyans and people of other nationalities waiting for evacuation. So far we have five killed and ambulances are rushing to the scene."
Another rebel spokesman, named as Abdelsalem, said the five killed were African migrant workers, but this was not independently confirmed.
Nato, which is enforcing a UN mandate to protect civilians in Libya, recently prevented pro-Gaddafi forces from sowing sea mines outside the harbour.
On Tuesday, a senior Libyan official warned that the army would do everything it could to block sea access to Misrata.
Misrata is the rebel's main stronghold in the west of the country, which remains largely under Col Gaddafi's control.
Earlier on Wednesday, International Criminal Court chief prosecutor Luis Moreno-Ocampo said he was seeking three arrest warrants in his investigation into crimes against humanity in Libya.
He did not give any names but told the UN Security Council that crimes were continuing.
In his report to the UN Security Council, Mr Moreno-Ocampo said that between 500 and 700 people were believed to have been killed in Libya in February alone.