DENVER (KDVR) — A person was able to get past security at Denver International Airport and board a passenger terminal train before being apprehended Monday, the airport said. The trains were shut down during the incident.

The individual was able to get down the escalators in the arrivals area around 12:30 p.m., according to the airport. The escalators lead to the underground airport trains.

One passenger who talked with FOX31 said plane boarding was also stopped. The airport says the security incident is being investigated.

The trains were back up and running at 1 p.m. The airport says all passengers and employees are safe.