An elderly couple sparked panic inside a plane when they whipped out a knife to peel fruits in the cabin.

The peckish pensioners boarded Vietnam Airlines flight VN208 headed to Hanoi and decided to skin some fruits shortly after taking off from Ho Chi Minh City, Vietnam on July 18.

To another passenger's surprise, they took out the 20cm-long prohibited item that somehow slipped past airport security, and nonchalantly began to use it.

The passenger, Luu Van Long, called the attention of a flight attendant, who promptly confiscated the item.

He said: 'I was shocked and wondered how they could carry knives on a plane. I waited for the take-off turbulence to settle down before pressing the button to alert the flight attendant.'

He added that the couple allegedly signed a document during the confiscation with the grandmother asking if she could get the knife back upon landing.

The Civil Aviation Authority of Vietnam (CAAV) has ordered a review of the airplane's security inspection following the incident.

To Tu Hung, head of the CAAV aviation security department, said: 'From the images of the video on social media, it's likely the knife in question is among the forbidden items.'

He added that airport staff deemed negligent may have their licenses revoked, and could face fines of up to 10 million VND (about 427 USD).

Meanwhile, the unwitting passengers may be fined between seven to 10 million VND (299 to 427 USD).