Italian prosecutors are investigating the deaths of 117 people in a shipwreck off Libya last month and whether delays at the rescue command centre in Rome cost lives.

The IMRCC (Italian Maritime Rescue Co-ordination Centre) in Rome was alerted at 1.40pm on 18 January to a dinghy in distress but said it fell under Libyan jurisdiction, despite receiving no response from the Libyan coast guard.

"There was a gap of three hours between the first sighting of the stricken dinghy by an Italian military aircraft" and the Libyan response, Agrigento assistant prosecutor Salvatore Vella said.

"There were many women in the boat, one holding a newborn, not more than two months old. Even getting help 10 minutes earlier can save a life," Vella said.

Italy's far-right Deputy Prime Minister Matteo Salvini has closed the country's ports to migrants and demanded Europe take its share.

Europe has been wrestling with divisions over how to handle the problem since the migration crisis of 2015 when more than one million people arrived on its shores, many of them fleeing conflict in the Middle East.

Italy has increasingly insisted Libya handle rescue operations off the North African country since a controversial accord was reached in 2017, with EU backing, to rebuild Tripoli's coast guard capacities.

The Agrigento prosecutors have delivered their initial investigation to Rome prosecutors, who will have to decide whether there is enough evidence for a trial of IMRCC officials for " failing to provide assistance".

The Agrigento team will continue its investigation against persons unknown for trafficking and aiding illegal immigration.

There were only three survivors of the disaster, each of whom told Vella of the nighttime departure at gun-point in crisis-hit Libya and the moment the weather worsened causing the overloaded dinghy carrying 120 people to start sinking.

"They had been given a satellite phone to call for help, but in the panic when the dinghy began to take on water, the 'captain' dropped it into the sea. It's not clear whether any call for help was ever made," Vella said.