LONDON (AFP) - London Luton airport was reopening on Monday after bomb disposal experts carried out a controlled explosion on a suspicious piece of hand luggage that had sparked an alert.

Some 1,600 passengers were evacuated from the airport earlier in the day, all flights in and out were cancelled and the main access roads to the terminal were shut off by police.

"There is no longer a security alert for us," a spokeswoman for Bedfordshire police said. "The bomb squad carried out a controlled explosion. It wasn't a bomb."

The airport's press office said in a tweet: "We are now working hard to re-open and get flights moving asap."

A spokesman for the airport earlier said 18 flights had been cancelled or diverted including by the low-cost airlines easyJet and Wizz Air, with most going to Stansted Airport.

Airport officials earlier said a "suspicious item" had been found in the passenger security checks area.

One eyewitness quoted on Sky News said the evacuation started calmly but became "chaotic" when airport staff hurried people out into the car park.

Passengers could be seen sitting outside next to their luggage, approaching police to ask when flights would resume.

"We understand passengers will be frustrated by the delays they are experiencing... we must ensure that the safety and security of all our passengers and staff remains our top priority," the airport said in a statement.

Luton is the fourth busiest airport serving London after Heathrow, Gatwick and Stansted and the fifth biggest in Britain.

Total passenger traffic last year was around 9.7 million people. Britain raised its terror alert level last month to "severe", meaning the authorities believe an attack is "highly likely".