A train driver died and at least 40 people were injured in a head-on train collision near Machu Picchu, Peru’s most popular tourist attraction.

Two trains collided on the single track leading to the ancient Inca city on Tuesday, according to a statement from local authorities.

It is said that 20 ambulances have arrived at the scene and the injured have been transferred to medical facilities in the nearby city of Cusco.

The U.S. Embassy in Peru said a U.S. citizen was injured in the crash, while the British Foreign Office said it was “supporting a number of British citizens involved” but did not specify their circumstances.

Local outlet Peru21 reported that “hundreds” of tourists remained at the site awaiting evacuation, with the terrain surrounding the crash site “impeding” evacuation.

A health official told Reuters that at least 20 of the injured were in serious condition.

The accident occurred on the track connecting Ollantaytambo station to Aguascalientes, the closest town to Machu Picchu. The journey between the two stations usually takes around 90 minutes.

The two trains involved in the accident are operated by PeruRail and Inca Rail respectively.

PeruRail said in a statement that “we deeply regret what happened,” adding that its staff “immediately” provided first aid to the train driver, conductor and passengers involved in the incident.

The cause of the accident has not yet been determined.

The accident comes amid an ongoing dispute between transport providers at the UNESCO World Heritage site, with local communities expressing dissatisfaction What they say is that the bidding process was not open enough.

The trains and buses that take tourists to the ancient town are expensive and, because of their accessibility, lucrative.

The ancient Inca city of Machu Picchu was built in the 15th century and is located in the Peruvian Andes. It is one of the seven modern wonders of the world.

Visitors can reach the site by taking a series of trains and buses, or hiking along the Inca Trail with a registered tour operator.

In 2011, officials imposed daily limits on visitors to protect and preserve the site, but concerns about overtourism remain.