At least six people have been killed in a train crash in southern Croatia.Police say another 20 people are in a serious condition with around 50 suffering light injuries. The passenger train was travelling between the Southern Adriatic city of Split and the Croatian capital of Zagreb when it derailed. Emergency teams are at the scene but rough terrain is believed to be hampering rescue efforts. The train was carrying around 90 passengers when it crashed at midday, local time. It was heading to the coast on a route often used by holidaymakers. The cause of the accident is still unknown.