ATLANTA, Georgia (CNN) -- Air traffic controllers were forced to use their personal cell phones to reroute hundreds of flights Tuesday after the Federal Aviation Administration's Memphis Center lost radar and telephone service for more than two hours, snarling air traffic in the middle of the nation.

The FAA's Memphis Center lost communication service Tuesday, affecting FedEx flights and others.

A spokesman for FedEx, which has its hub in Memphis, Tennessee, said the package delivery company had diverted 11 aircraft to other cities. But most of its flights take off and land after 10 p.m., so FedEx expected the impact to be minimal, the spokesman said.

Air traffic was halted at 12:35 p.m. ET when a major communication line that feeds all the telephones at the FAA's Memphis Center failed, said FAA spokeswoman Kathleen Bergen.

Service was restored at 3 p.m.

The malfunction, which occurred inside a telephone company's switching office, made it impossible for air controllers at FAA's Memphis Center to communicate normally with adjoining centers to hand off control of flights, Bergen said.

In addition, three of nine long-range radar systems were lost, causing the FAA to temporarily ground traffic within a 250-mile radius of the center, affecting flights in seven states, Bergen said.

Adjacent centers in Atlanta, Georgia; Indianapolis, Indiana; Kansas City, Missouri; and Fort Worth, Texas; were pitching in to try to reroute planes, she said.

There was no indication the failure was deliberate, she said.

Doug Church, a spokesman for the National Air Traffic Controllers Association, called the failure "a major safety problem."

At the time of the outage, controllers "were thrust into an immensely chaotic situation in which they had to use personal cell phones to talk to other air traffic control facilities about specific flights that they could not communicate with themselves," he said.

"Significant delays" resulted at airports in the middle of the country, including Dallas-Fort Worth, Atlanta and Charlotte, North Carolina, he said.

Memphis Center's airspace includes 100,000 square miles of airspace, covering Tennessee, Arkansas, Mississippi and parts of Alabama and Kentucky.

Church predicted that flight operations in the affected area "are not going to be 'normal' for quite some time."

A spokesman for Northwest Airlines said the impact on the airline was "pretty minor," with 13 flights canceled and 19 others diverted out of 740 scheduled flights for the day.

A spokeswoman for Delta Air Lines said it canceled six flights and rerouted several others as a result of the incident. E-mail to a friend