An Indian-origin British Airways passenger onboard a flight from London to San Francisco was caught groping a woman's breast for five minutes while she slept on her seat, reports said.

The incident occurred on April 15 while the passenger was charged in US on April 22.

According to the police complaint, the woman was sleeping when co-passenger Vinay Pochampally who was seated right behind her, reached over from behind, placed his hand down her shirt while other passengers watched.

Pochampally allegedly put his hand down the shirt of the passenger and had his hand underneath her shirt and underwear "for approximately four to five minutes, making skin-to-skin contact in the breast and upper chest area of the passenger, before she awoke", the US District Court criminal complaint said.

The incident occurred about two hours into BA Flight 285 on April 15 and Pochampally was allegedly intoxicated at the time.

The passenger woke up, allegedly to find Pochampally's hand inside her shirt and touching her breast. The accused then "quickly removed his hand and ran away down the aisle. Multiple passengers witnessed the incident and notified the British Airways flight crew of what had just occurred", according to the complaint.

British Airways staff confronted Pochampally on learning of the molestation from passengers, police said.

They ordered him to move to a different seat for the remainder of the 10-hour trip and contacted law enforcement upon landing at San Francisco International airport.

Pochampally was charged with simple assault. He faces up to six months in prison if convicted, along with a $5,000 fine and five years' probation.

It is not clear yet if Pochampally is a US citizen.