A warship taking part in a NATO-enforced naval embargo on Libya came to the rescue of an overcrowded boat with its engine cut off in the Mediterranean, a NATO spokesman said.

"A NATO vessel received an SOS signal and responded to a vessel that is dead in the water with no functioning engine and is overcrowded," said David Taylor, speaking from the operation's command headquarters in Naples.

Taylor said the boat had requested further aid, without adding more details.

The United Nations warns that the crisis in Libya could displace up to 250,000 refugees and migrants, and boatloads with thousands of mostly Tunisian migrants have been arriving on Italian shores in recent weeks.

Boats carrying migrants are mostly ageing and overcrowded and their captains often cut off the engine when coast guards arrive so as not to be identified.

Many of the boats arriving recently have carried around 100 people each.

ANSA news agency yesterday reported that a boat that left Libya carrying 330 Eritrean migrants had gone missing and today it said that a Canadian warship was monitoring another boat that left Libya overnight.