European countries have come to an agreement on how to share responsibility for 131 migrants who were blocked on board a coastguard vessel by Italian authorities.

An EU Commission spokeswoman told AFP that France, Germany, Ireland, Luxembourg and Portugal would join the Italian church in caring for the migrants.

Italy's anti-immigrant deputy prime minister Matteo Salvini said he would allow the migrants rescued last week - now being held on a coastguard boat - to disembark "within hours".

"I will give authorisation (for the migrants) to disembark in the coming hours," the far-right minister wrote on Facebook.

The Commission did not give a breakdown on how the migrants would be shared between host countries, but the official said most would stay in Italy.

Some 140 migrants, who set off from Libya in two boats, were picked up by Italian patrols and transferred to the coastguard ship Bruno Gregoretti.

The operation took place on the same day that at least 115 other migrants were feared drowned in a shipwreck off Libya - according to the International Organisation for Migration (IOM).

Several migrants aboard the Gregoretti have already been evacuated for medical attention, including a seven-month pregnant woman, her two children and her partner.

But Salvini had insisted that the remaining migrants would not be able to leave the vessel until other European countries agree to take them in.

Salvini, also interior minister, has taken a hard line against migrants rescued at sea being brought to Italy, which he says bears an unfair burden in the crisis.