A Southwest Airlines flight to Las Vegas had to dive to avoid hitting another plane midair … and now a couple flight attendants are nursing injuries.

Passengers on a Friday flight from Burbank to Las Vegas say their pilot had to dive aggressively to avoid a midair collision shortly after takeoff … sending passengers flying out of their seats, with some bumping their heads on the cabin ceiling.

Comedian Jimmy Dore was on the flight and he says the pilot came on the PA system and told passengers his collision warning alert went off and he needed to avoid a plane coming at them.

Southwest Airlines tells TMZ … the crew “responded to two onboard traffic alerts Friday afternoon while climbing out of Burbank … requiring them to climb and descend to comply with the alerts.”