Heathrow Airport cancelled 38 flights on Saturday as it recovered from a computer glitch that wreaked havoc with the London airport system, the world's busiest hub.

"There are 38 flights cancelled today as a result of (the computer fault)," said a Heathrow spokesman said, adding that 1,300 flights were scheduled Saturday to and from the airport.

Departures were blocked for more than an hour on Friday and arrivals diverted when NATS, Britain's main air navigation service, restricted traffic volumes because of a problem that has "not been seen before".

The system failure occurred at the state-of-the-art £700 million ($1 billion, 880 million euro) Swanwick control centre near Portsmouth on the southern English coast.

In a statement released Saturday, NATS said the problem occurred when trying to switch workstations between the "standby" and "on" states.

"In this instance a transition between the two states caused a failure in the system which has not been seen before," it said.

"The failure meant that the controllers were unable to access all of the data regarding individual flight plans which significantly increases their workload.

"The controllers had a full radar picture and full communications with all aircraft at all times during the incident and at no time was safety compromised in any way," it added.

Despite having full radar capabilities, NATS "immediately took steps to reduce the traffic into and out of the UK network" in order to "maintain a safe operation for the flying public."

The London airports system, grouping Heathrow with Gatwick, Stansted and Luton, is the busiest hub in the world with around 135 million passengers a year.

London's Heathrow alone is Europe's busiest in terms of passenger numbers, and the world's busiest for international passenger traffic.

Hundreds of flights in Britain and Ireland were delayed or cancelled last year because of a similar problem.

Transport minister Patrick McLoughlin called the disruption "simply unacceptable" and said he had asked NATS for a full explanation.

"I also want to know what steps will be taken to prevent this happening again," he added.