Donald Trump's visit to Sicily's Taormina for the G7 summit is a "security nightmare" and it's reportedly driving Italian authorities "mad".

Taormina's roads are too narrow and bendy for the US president's car and his motorcade longer than the distances it would have to cover during the summit, Italian newspaper La Repubblica said on Tuesday.

The American secret service has been inspecting the roads of the former Arab fortress ahead of the May 26-27 summit, and are finding danger wherever they look, according to Italian media.