A Southwest plane carrying passengers and a FedEx cargo jet came within 100 feet (30 metres) of each other at a Texas airport in a dramatic near miss.

The FedEx plane was attempting to land at Austin-Bergstrom International Airport on Saturday morning (local time) but had to change course after a second plane was cleared to depart from the same runway, according to the Federal Aviation Administration.

"The pilot of the FedEx plane discontinued the landing and initiated a climb out," the FAA said in a statement.

The Boeing 767 cargo plane was several miles from the airport when it was cleared to land, according to the FAA. But just before it was expected to land, an air traffic controller gave the go-ahead for an airplane operated by Southwest Airlines to take off.

Today, Jennifer Homendy, chairwoman of the National Transportation Safety Board, told CNN the two planes came as close as 100 feet (30 metres) from colliding.

"The FedEx pilot told the Southwest crew to abort taking off," she said.

"I’m very proud of the FedEx flight crew and that pilot," Homendy said. "They saved, in my view, 128 people from a potential catastrophe.

"It was very close, and we believe less than 100 feet."

In a statement to The Associated Press, the Austin-Bergstrom International said it was "aware of the Federal Aviation Administration’s investigation into the discontinued landing of a flight. We will assist our FAA partners and their investigation as necessary."

A similar close call was averted at John F. Kennedy International Airport last month after an American Airlines plane crossed a runway while a Delta Air Lines' Boeing 737 plane was preparing for takeoff. The Delta plane stopped about 1000 feet (about 0.3 kilometres) from where the American Airlines plane had crossed from an adjacent taxiway, according to the FAA statement.

Austin-Bergstrom is about 5 miles (8 kilometres) southeast of downtown Austin.