London's Heathrow Airport said on Monday it was open and fully operational, Reuters reported.
The announcement came a day after a fire knocked out power and forced Europe's busiest airport to close.
The closure of Heathrow has caused travel chaos around the world.
Heathrow is the world's fifth-busiest airport and was forced to halt operations after a fire engulfed a substation near the airport last night.
The closure has not only caused inconvenience to passengers but has also sparked outrage among airlines, who have questioned how such critical infrastructure could fail. Companies are now facing financial consequences worth millions of pounds and there is likely to be a dispute over who will have to pay, notes Reuters.
Police said there was no indication of foul play, but added that they would look into all possibilities and that counter-terrorism officers would lead the investigation, given the critical importance of the infrastructure.
Aviation experts said European airports had not experienced such widespread disruption since an Icelandic volcano erupted, sending up a huge ash cloud, causing around 100,000 flights to be cancelled.