Spain is to send a warship to pick up around 80 migrants stranded for more than two weeks on board a charity rescue vessel off Italy, as around a dozen threw themselves into the sea in a desperate bid to reach dry land.

The migrants will be collected and taken to Mallorca, a journey of 600 miles that will take at least three days.

The Open Arms rescue ship has been in limbo at sea for 19 days, with its crew warning that conditions on board were becoming increasingly untenable, as tensions broke out over access to shade and the vessel’s two lavatories.

The situation was further complicated on Tuesday, when an Italian prosecutor ordered the migrants disembark in Sicily.

Luigi Patronaggio also ordered the vessel preventatively seized after inspecting the boat on and "given the difficult situation on board," a judicial source said.

Since Thursday, the vessel has been anchored a short distance from the tiny Italian island of Lampedusa.

At least a dozen migrants jumped into the sea on Tuesday and tried to swim towards the island.

Italian coast guard officers leapt in after them and the migrants were reportedly taken to Lampedusa.