LONDON (AP) — British authorities are investigating how a Sudanese migrant managed to walk nearly the entire length of the 31-mile (50-kilometer) Channel Tunnel from Calais before being stopped.

Kent police say Abdul Rahman Haroun, 40, has been charged with causing an obstruction to an engine or carriage using the railway. He allegedly slipped past officers at the entrance of the tunnel and dodged hundreds of security cameras before being spotted by British security guards near Folkestone on Tuesday.

Eurotunnel described the incident as being extremely dangerous, with trains travelling up to 100 miles (160 kilometers) an hour.

Authorities have increased security, fence and border patrols amid an unprecedented surge this summer in migrants trying to reach Britain from France.