Italy and Germany are utterly opposed to Austria's plan to build a fence at its border with Italy, Italian Prime Minister Matteo Renzi said on Thursday after talks with German Chancellor Angela Merkel.

"We expressed our total opposition to, and, in some ways, our shock over the position that has been taken by our Austrian friends," Renzi said during a joint news conference with Merkel in Rome.

Austria has said it plans to erect a fence at the Brenner crossing it shares with Italy to "channel" people. Brenner is one of the border points that migrants use as they head towards wealthy northern Europe.

Austrian Interior Minister Wolfgang Sobotka said in Rome last month that as many as a million migrants were poised to cross the Mediterranean from Libya this year. Italy says the figure is much lower, though calm summer seas may well bring a surge.