BERLIN (AP) — Swiss police say a German bus has crashed into a metal road sign on a highway in southern Switzerland, leaving several passengers seriously injured.

Ticino canton (state) police said the bus was heading south with about 40 people on board at the time of the accident Sunday morning at Sigirino, on the A2 highway near Lugano. The highway is part of a major route across the Alps from northern Europe to Italy.

Police said several people were seriously hurt and some were still trapped in the vehicle. The highway was closed down for the rescue operation.

The cause of the crash wasn't immediately clear.