Passengers were asked to wait in designated areas outside Terminal 2 while police were seen at the scene, Wales Online reports.
A terminal building at Heathrow Airport has been evacuated as police are struggling with a security breach.
Passengers were asked to leave the building after suspicion arose in Terminal 2.
Another wrote: “Search operations at HeathrowAirport Terminal 2 underway due to security alert all passengers and staff evacuated sniffer dogs even on duty”.
One Twitter user said: “Some sort of security alert at Heathrow Terminal 2 – I’m not sure what happened at this stage, but the passengers have gone outside.
Travellers reported that sniffer dogs had also arrived on the scene, reports The Mirror.
Heathrow Airport said in a statement: “Our teams are working with the police to respond to a possible suspicious object identified in Terminal 2.
A third wrote: “Some sort of security alert in Heathrow Terminal – I’m not sure what is happening at this stage, but passengers have moved outside”.
Staff were reportedly let back in at 13.45.
“As a precautionary measure, passengers were temporarily removed from the area. We apologize to all passengers who have been inconvenienced during the investigation of the matter.