A serious train collision near Machu Picchu, Peru’s popular Inca site, killed one train driver and injured at least 40 people. The accident happened on Tuesday on the single track between Ollantaytambo Station and Aguas Calientes, the closest town to Machu Picchu. The local government confirmed the crash and said 20 ambulances rushed to the scene. Injured people were taken to hospitals in nearby Cusco city. The US embassy reported that US citizens were among the injured, while police have not confirmed identities yet. Local media Peru21 said hundreds of tourists remain stranded, as rescue is difficult due to the rough land around the crash site. A health official told Reuters that at least 20 injured people are in serious condition. The trains were operated by PeruRail and Inca Rail. PeruRail said, "We deeply regret what has happened" and added their staff gave immediate first aid to the victims. The cause of the crash is still unknown. The accident comes during tensions over transport service bids to the UNESCO heritage site. Locals say the bidding is not open and prices for trains and buses to Machu Picchu are high, as transport is limited and popular. Machu Picchu, built in the 15th century, is one of the Seven Modern Wonders of the World. Visitors usually reach it by train and bus or by hiking the Inca trail with tours. Since 2011, visitor numbers have a daily limit to protect the site, but concerns about too many tourists remain.