Stansted Airport has confirmed to ITV News that two RAF jets have accompanied a plane, which has now landed at the airport.
It follows earlier reports of a loud bang heard in the Kent area around 4:40pm today.
A man who has been arrested at Stansted airport on suspicion of being involved in terrorism offences was returning from Istanbul, Turkey.
Officers for the Metropoiltan Police's Counter Terrorism Command stopped the 21-year-old at 8.40pm on Sunday 19 January following his return from Istanbul via Stuttgart, Germany.
He was subsequently arrested by officers at 1.10am today and taken to a London police station where he remains in custody.
The arrest was not in response to any immediate threat or risk.
Detectives have carried out searches of three addresses in connection with the investigation, Scotland Yard said.
A 21-year-old man has been arrested at Stansted Airport on suspicion of being involved in the commission, preparation and instigation of terrorism offences, Scotland Yard said.
A Stansted spokesman said flights were landing again from around late morning, after a period of around three hours when no touchdowns were possible.
Stansted Airport has said flights will be subject to delay and cancellations and is advising passengers to check their flight status on its airline website.
In a statement, the airport said NATS, which is responsible for the operation and maintenance of the ILS equipment, have engineers on site and are currently working to the resolve the issue and return the airfield to normal operations as quickly as possible.
Due to a technical problem with the landing system at Stansted and low visibility weather conditions, flights are currently unable to land at the Essex airport, Ryanair said.
Stansted Airport has said on Twitter that it is dealing with a power outage which is "impacting fight operations" at the London airport.
Lightning strikes have disrupted train services to Stansted Airport this morning:
Heathrow Airport Holdings - the company formerly known as BAA - had its ownership of Stansted brought into question when the Office of Fair Trading referred the company's holding to the Competition Commission (CC).
After a long inquiry the CC ruled that BAA's airport ownership was uncompetitive.
The commission ruled in 2009 that BAA must sell Gatwick and Stansted and one of either Edinburgh or Glasgow airports. Gatwick had already been sold by the time of the ruling and since then BAA has sold Edinburgh.