About 250 people are missing in the Mediterranean after the vessels carrying them illegally to Europe got into difficulty off the Tunisian coast, a Tunisian security official told Reuters on Thursday.

Tunisian coastguards and military rescued 570 people, but many others went into the water when a stampede to get off the small fishing boats -- combined with the effect of rough seas -- capsized some of the vessels, the official said.

"Search operations are still continuing... About 250 people are missing," said the official from the southern Tunisian port of Sfax, where the survivors were taken. "We haven't found a single body so far."

"Five hundred and seventy people have been rescued. Most of them are in good health and they are in the military barracks in Sfax and some are in hospital. Among those who were hospitalised, three have died," he said.

"They are all of African nationalities and they were on small fishing boats," said the official, who was speaking on condition of anonymity.

The boats encountered problems on Tuesday about 20 km (12 miles) off the Tunisian island of Kerkennah as they headed for Italy, the TAP state news agency said. They were carrying refugees who were fleeing the violence in neighbouring Libya.

Thousands of people fleeing upheavals in North Africa have been heading to Italy on rickety boats in recent months, creating an immigration crisis in Lampedusa, an Italian island situated half way between Tunisia and Sicily. – Reuters