The airport was closed about 9:10 p.m. and about 85 flights were canceled or diverted, according to Karen Pride, spokeswoman for the Chicago Department of Aviation. Electrical power was restored to the runways at 1:19 a.m., Pride said.
Pride advised people to contact airlines for the status of flights this morning.
ComEd spokeswoman Martha Swaney said the cause appeared to be an equipment failure at the airport, but had no details.
The terminals were not affected, and Pride said airport officials escorted aircraft back to the terminal building to allow passengers to get off planes.
But passengers lit up social media networks including
"Sitting on tarmac for almost two hours, runway lights keep flickering but won't stay on...not looking good," said one person.
"I'm stuck on the tarmac. Hot. Sweaty. Frustrated. And hot. Pray for good customer service," said another passenger.