One of the closed runways, 1-R, has reopened but crews are still working to patch up 28-L.
"Our airfield safety officers were doing a routine inspection of our runways and noticed about a 12-inch depression on runway 28 left. This is the type of thing where, if a plane went over it, you would feel a bit of a thump. Out of an abundance of caution, we closed the runway," said spokesperson Doug Yakel.
Passengers say having your flight canceled is one thing. But when they found out why their flights were canceled, they say that was the real surprise.
"A little concerning and once you get here and see all the workers it's like, what's going on," said Ashley Thomas, who said her flight to Phoenix was canceled.
"We heard there is a big pothole in one of the runways and so we are just wondering, is someone checking the runways all this time?" asked Jeannette Gonzalez whose flight to Southern California was canceled.
Delays were about 30 minutes to an hour long in the morning but were expected to increase as the impact spread. Some flights were canceled.
"It'll cause delays like we see on a bad weather day," said Yakel.
Crews could be seen on the runway pouring asphalt into the hole. They then have to wait for it to cure. They estimate that they can reopen the runway by mid-afternoon.
This runway was already scheduled for improvements this Fall. The plan is to add a concrete layer beneath the surface, which officials say could help prevent this from happening in the future.
RELATED: Runway repairs at San Francisco International Airport may cause flight delays in September 2019
Alaska Airlines has two planned flight diversions scheduled today so far. This is typical for Alaska when SFO goes into any traffic management program, an airport spokesperson said.
The line at the Southwest Airllines counter at SFO where agents are trying to rebook passengers. Some flights were cancelled - others delayed- because of a pothole in a runway. It is closed- airport is down to one runway right now. pic.twitter.com/9ZpAmHWb2S— Amy Hollyfield (@amyhollyfield) April 11, 2019