Technical issues cause underground trains at Denver International Airport to run at limited capacity

UPDATE: Service was fully restored​ for the underground trains at Denver International Airport early Wednesday morning.

The underground trains to the concourses at Denver International Airport are running at limited capacity. That's according to airport officials, who said on Tuesday morning that technical issues are to blame. They said buses are being used to take some passengers from the terminal to their concourses.

The disruption has meant much longer than usual wait times to board the trains, and long lines. One traveler said she had to wait for an hour to get on a train. The airport encourages flyers to be at the airport at least 30 minutes earlier than they planned to be there because of the issue.

Passengers who are flying out of Concourse A are encouraged to use the A checkpoint and walk across the bridge to get to their gate.

"Passengers will either be guided by DEN staff to board a train or to take a bus from Concourse A to concourses B and C," the airport tweeted just before 10:30 a.m.

So far it's not clear what the technical issues are, but engineers at the airport were working to resolve them.

The technical issues are expected to affect operations throughout the day on Tuesday.