Hundreds are now feared dead after another boat, said to be carrying out between 500 and 700 migrants, overturned off Libya.

The incident occurred some 200 km south of the Italian island of Lampedusa, according to Italian coastguard officials quoted by the BBC.  

As many as 28 migrants have been rescued, according to the website of the Time of Malta news outlet (Malta is located not far from Lampedusa).

The edition reports that migrants moved to one side of the boat to draw the attention of a passing merchant ship. This seems to have caused the boat to capsize.

This week alone there have been several other incidents involving migrants who tried to flee North Africa. On Wednesday, a boat carrying about 550 migrants overturned off the Lybian coast, leaving about 400 of them dead.

Italian coast guard officials say some 10 000 migrants have been rescued between this Monday and Thursday alone while trying to reach Italy across the Mediterranean, but another 900 are thought to have drowned.

This has been the most intense influx of asylum seekers since the beginning of the year. For the past three-and-a-half months, at least 31 500 migrants have entered Italy and Greece seeking to escape from the civil war in Libya and the instability elsewhere in Africa.

UNHCR spokesperson William Spindler told the BBC that Sunday's incident could be the largest loss of life in a single incident on record.