A domestic flight attendant ended her shift in hospital with missing teeth, after a passenger knocked her out.

A Southwest Airlines flight from Sacramento to San Diego quickly became the subject of a police investigation after a fight started between a stewardess and a passenger on May 23.

The unidentified flight attendant had asked Vyvianna Quinonez and her family members to put their face masks back on during the journey. However, the 28-year-old traveler allegedly refused and the matter quickly escalated to a heated exchange.

“It was so unnecessary [and,] in the first altercation, she had said that she was going to call the captain,” witness Michelle Manner, who was sitting two seats in front of them, told FOX40. “She should have just stayed there in her back cubby but she came back out screaming at them again.”

Quinonez allegedly became upset then warned the flight attendant not to make physical contact with her.

“Vyvianna had said to her three times that we could hear, ‘Get off of me, quit touching me [and] get your hands off of me,'” Manner said according to the broadcaster.

The witness claims she recorded a video of the rest of the dispute during which Quinonez punched the flight attendant before another passenger intervened. The force allegedly detached two of the stewardess’s teeth.

“The flight attendant continued to yell and, I mean, she was yelling,” she said. “We got to the point to, where we are like, should we start videoing this?”

Southwest Airlines vigorously defended the flight attendant’s professional conduct, and suggested the passenger could have easily avoided making a scene.

“[The customer] repeatedly ignored standard inflight instructions, and became verbally and physically abusive upon landing,” a Southwest representative said in a statement obtained by the New York Post.

The Port of San Diego Harbor Police Department is investigating the incident and believes there is credible evidence to prove Quinonez indeed attacked the stewardess.

“According to witnesses, an altercation between a passenger and a flight attendant had taken place during the flight,” police said in a statement obtained by USA Today. “During the altercation, the passenger struck the flight attendant, causing serious injuries.”

Quinonez was charged with violence resulting in serious injuries, and detained until she finally paid the $35,000 bond. The accused maintains she acted in self-defense without providing further details unless a lawyer is present.

The flight attendant was transported to a San Diego hospital emergency room for urgent treatment before being released.

The Southwest Flight Attendants Union (TWU Local 556) described the incident as a classic example of the kinds of safety hazards airline staff face each day on the job.

“This unprecedented number of incidents has reached an intolerable level, with passenger noncompliance events also becoming more aggressive in nature,” TWU Local 556 President Lyn Montgomery said in a statement.

“This past weekend, one of our flight attendants was seriously assaulted, resulting in injuries to the face and a loss of two teeth. Unfortunately, this is just one of many occurrences … [and] we cannot tolerate our beloved co-hearts being abused in such a manner,” she added.

Southwest reported 477 misbehaving passengers between April 8 and May 15, according to the union.

The Federal Aviation Administration recently responded to an increase in misbehaving travelers through introducing a zero-tolerance policy in January. The rule was extended in March until the pandemic ends according to USA Today.