London’s Heathrow Airport reopened on Saturday after a power outage at one of the world’s busiest airports the previous day caused widespread chaos and cancellations.

A post on the airport’s website on Saturday said “flights have resumed at Heathrow, and we are open and fully operational. Teams across the airport continue to do everything they can to support passengers impacted by yesterday’s outage at an off-airport power substation.”

The airport also said in a statement that “We have hundreds of additional colleagues on hand in our terminals and we have added flights to today’s schedule to facilitate an extra 10,000 passengers traveling through the airport.”

On Friday, a fire at an electrical substation cut power to the airport for most of the day. The outage affected more than 1,300 flights to and from Heathrow and disrupted travel for more than 200,000 passengers. The outage also cut power to over 16,000 homes in the area. 

The ripple effect of the transportation hub shutting down for over 16 hours was immediate. About 1 million Americans travel through Heathrow each month.

“The pilot came on and said some of us may have noticed that the plane was turning around, not to be alarmed, but London Heathrow was closed due to a fire,” said Justin McLane, who flew from Boston. 

Meanwhile, pressure mounted on airlines and Heathrow to take care of passengers. 

“Contingencies of certain sizes we cannot guard ourselves against 100%, and this is one of them,” said Thomas Woldbye, Heathrow’s chief executive. “This has been a major incident. I mean, short of anybody getting hurt, this is as big as it gets for our airport and we are actually coming back quite fast.”

While some travelers and officials are calling for an investigation into the blaze, police say there is not early indication of foul play. Given the large impact the fire had on national infrastructure, counterterrorism police are leading the investigation.

The latest numbers from travel data provider OAG Aviation show Heathrow is the fifth busiest airport in the world this month. Earlier this year, it reported its busiest January on record, serving over 6.3 million passengers and averaging over 200,000 passengers a day. More than 1.2 million of those passengers traveled between the U.K. and the U.S.