ROME (AFP) - Italy's navy has rescued 233 mostly African immigrants from a boat in trouble off the coast of the Mediterranean island of Lampedusa, the scene of two shipwreck tragedies last year.

The 10-metre-long wooden boat was sighted by a navy helicopter in choppy waters on Wednesday with immigrants from Eritrea, Nigeria, Somalia, Pakistan, Zambia and Mali aboard, including seven women.

"Considering the rough seas, the overcrowded boat and the precarious conditions, a situation of emergency was declared," the navy said in a statement.

The immigrants were rescued by the destroyer San Marco before being transferred to a frigate which was ferrying them to Sicily, where they were expected to arrive on Thursday.

The Italian government has launched a major operation called "Mare Nostrum", mobilising warships, amphibious vessels and aircraft to try and prevent further tragedies like the two shipwrecks in October in which more than 400 immigrants died.