VARAZDIN, CROATIA (REUTERS) - Twelve people were killed in Croatia on Saturday (Aug 6) when a Polish bus filled with religious pilgrims slipped off a road and crashed near Varazdin, authorities said.

Thirty-two people were injured in the crash which happened at 5.40am (11.40am Singapore time) on the highway between Varazdin, in north-west Croatia, and capital Zagreb.

Croatian Health Minister Vili Beros said 19 people were in a serious condition.

Marcin Przydacz, deputy head of the Polish Foreign Ministry, who was travelling to the site on Saturday, said the injured were being treated at five hospitals in Croatia.

He said there were 44 Polish pilgrims on the bus driving from Poland to Medjugorje, a Roman Catholic shrine in southern Bosnia, including two drivers.

Among them were three priests and six nuns, a ministry spokesman said.

Police cleared the area where the accident took place after firefighters and medical teams recovered all the occupants of the vehicle which had Warsaw registration plates.

Polish police officers, in Croatia as part of project "Safe Tourist Destination" project, were helping Croatian authorities in communicating with the survivors.

An investigation has been started into the cause of the accident.