A Southwest Airlines plane rapidly dropped in elevation after departing from the Los Angeles area on Friday, with passengers posting online that the pilot was forced to rapidly change course to avoid a potential collision with another aircraft.

Flight 1496 from Hollywood Burbank Airport to Las Vegas plummeted rapidly, lifting passengers out of their seats and injuring two flight attendants.

The crew "responded to two onboard traffic alerts... requiring them to climb and descend to comply with the alerts", Southwest said in a statement.

The Federal Aviation Administration (FAA) said it was investigating the "incident". It comes less than one week after a similar near-miss.

"Ensuring the safety of everyone in the national airspace system remains our top priority," the FAA statement added.