MILAN - Eight Tunisian migrants have died and a further 20 are believed to be missing after a Tunisian naval ship collided with a wooden boat packed with migrants, the U.N. migration agency said Monday. Tunisian authorities said 38 people were rescued.

The Tunisian defence department said in a statement that the collision happened Sunday about 54 kilometres (30 miles) off the coast of El Ataya, on the island of Kerkennah. The circumstances remain unclear.

Maltese authorities co-ordinated the rescue with the assistance of the Italian and Tunisian navies.

The exact numbers on board were unknown, but Flavio Di Giacomo of the International Organization for Migration said it is believed that the boat was carrying around 75 Tunisian migrants.

The number of Tunisians making their way from Tunisia to Italy is on the rise, although the reasons are not clear. IOM says that 1,400 Tunisians arrived in Italy last month alone, compared with 1,357 in the first eight months of the year.

But that is only those who have been officially counted.

Non-governmental organizations in Sicily estimate that three times that many have arrived since June, most in wooden boats that get left on the shore.

"We have documented around 80 boats left on the beaches from June through today, since the route from Libya was interrupted," Claudio Lombardo of the NGO Mareamico told Sky TG24, referring to a decrease in number of sea rescues since Italian authorities reached deals with Libyan players to reduce migrant trafficking.

He said they estimate at least 3,000 North Africans had arrived on the boats, of whom authorities have detained just 400. The rest have disappeared, presumably moving on in search of work and earning the moniker "ghost arrivals."

Di Giacomo said the reason for the spike in arrivals from Tunisia is unclear, but that it could be the result of an economic crisis that has pushed Tunisians to try to find work in Italy after the end of the summer tourism season in northern Africa. He said that so far those coming don't appear to be sub-Saharan Africans seeking a new route to Europe.

So far this year, IOM says 2,658 migrants have died or gone missing trying to cross the Mediterranean Sea in rickety smugglers' boats, almost all of those trying to reach Italy. That compares with 3,682 overall last year.

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Stephen Calleja in Valletta, Malta, and Jamey Keaten in Geneva contributed.

News from © The Associated Press, 2017