Stansted Airport's train station has been evacuated after reports fire alarms were sounding throughout the building.
The alarm ended within an hour and service resumed, but the incident caused delays.
Disruption to Stansted Express trains was expected until 18.15, the service said in a Twitter post.
Stansted Express referred delayed customers to compensation information, but social media users voiced frustration that they could miss flights because of the incident.
One Twitter user called Amy asked: "What happened if you miss your flight because the train was stuck?"
She added: "My sister-in-law was stuck on a train outside Stansted because of the alarm and will likely now miss her flight."
