SAN DIEGO, California (CNN) -- Two airliners were ordered to make sharp turns to avoid a midair collision Monday afternoon.

While a spokesman for one of the airlines involved said no one was in danger, a spokesman for the air traffic controllers union said the jets were within eight seconds of colliding.

The Federal Aviation Administration has termed the incident an "operational error."

FAA spokesman Mitch Barker said Delta Airlines Flight 550 and Alaska Airlines Flight 257 came within 2.5 miles of each other while flying 30 miles southeast of Julian, California, in San Diego County.

The standard separation of aircraft is normally five miles. The distance between the two aircraft was "less than standard separation," Barker said.

The Delta flight, bound for Atlanta, was being rerouted southward to avoid thunderstorms around Los Angeles. The Alaska Airlines jet was inbound to Los Angeles from Mazatlan, Mexico.

Barker said supervisors stepped in to help the air traffic controller when the two planes entered the same area.

The Delta and Alaska flights were quickly ordered to turn sharply to avoid a collision, Barker said.

Barker declined to speculate on a cause for the incident, saying it is still under investigation.

The Delta crew did not file a report about the incident, and company officials were unaware of it until receiving a call from a reporter, said Delta spokesman Bill Berry. Delta then contacted the FAA and was told the incident is being investigated.

Alaska Airlines spokesman Lou Cancelmi said that although the two aircraft came within a "couple of miles" from each other, "no one was ever in any danger."

Cancelmi said both aircraft crews were aware of each other's position because of onboard anti-collision equipment, known as T-CAS. He is trying to get more information from the flight crew.

Hamid Ghaffari, a spokesman for the National Air Traffic Controllers Association in Los Angeles, said the two jetliners were so close "there could have been a loss of life." He said the two planes were moving toward each other at a combined speed of 1,000 knots (1,115 miles per hour) and were within eight seconds of colliding.