Flights were snarled at the Middle East's busiest airport in Dubai early Wednesday after a backup system needed to deal with heavy fog failed, forcing airlines to divert dozens of planes.

The airport operator, Dubai Airports, said it shut the facility's two runways during the busy morning rush at 6:45 a.m. About 50 flights were rerouted to other airports in the region, including Abu Dhabi, Dammam in Saudi Arabia, and the Omani capital Muscat.

Chris Garton, the airport operator's senior vice president for operations, said the problem was a loss of power to a backup system needed to keep runway lights working. Although the main electrical supply was not cut, authorities decided to halt flights as a precaution because of dense fog that had settled over the city.

"We like to have a backup for reasons of safety," Garton said.

The fog later cleared and flights resumed less than two hours later, though officials said it would take time to clear the backlog of delays.

Rapidly expanding Dubai International Airport is the region's largest air hub, and the world's fourth busiest in terms of international passenger traffic. It handled 37.8 million passengers in the first eight months of this year.

Garton described the power cut as unusual and said the cause is under investigation. The airport's main power supply comes from the city's electrical grid, though backup electricity is produced on site, Garton said.

Many of the flights listed as diverted or delayed belonged to Dubai-based Emirates, the region's largest carrier. The airline was not immediately able to say how many flights were affected, but says it regrets any inconvenience caused.

Several flights were also listed as delayed at the nearby airport in Sharjah, which is home to budget carrier Air Arabia. It did not respond to a request for comment.

Dense morning fog is not uncommon in the United Arab Emirates, particularly in the autumn and spring. Local media reported numerous traffic accidents on the busy main highway between Dubai and Abu Dhabi, which has been the scene of deadly chain-reaction pileups in recent years.