Singapore Airlines (SIA) has reassured passengers that small cameras attached to the in-flight entertainment system on some of its planes are not being used.

Some customers were concerned that they were being monitored as they watched movies and used other entertainment options on their journeys.

However, an SIA spokesman told The Straits Times: "The camera is permanently disabled and cannot be activated on board."

The in-flight entertainment systems installed with a camera are manufactured by Panasonic and Thales, and can be found on the Airbus 350, A-380, Boeing 777-300ER and B787-10 planes, the airline said.

"These newer in-flight entertainment screens and handsets are provided by the original equipment manufacturers," the spokesman said.

"Do allow us to reiterate that we have no plans to enable or develop any features using the cameras."

The same Avant in-flight entertainment system developed by French aerospace firm Thales has been ordered or installed on more than 1,600 aircraft by major carriers, Thales says on its website.

They include Japan Airlines, Emirates, American Airlines, China Southern Airlines and Hainan Airlines.

Passenger Vitaly Kamluk, who spotted the camera on a recent SIA flight, said in a tweet: "Just found this interesting sensor looking at me from the seat back on board of Singapore Airlines.

"Any expert opinion of whether this (is) a camera? Perhaps @SingaporeAir could clarify how it is used?"

The airline replied to him with the same assurance that "there are no plans to develop any features using the cameras".

SIA added: "We would like to share that some of our newer in-flight entertainment systems provided by the original equipment manufacturers do have a camera embedded in the hardware."

Still, some suggested that the cameras should be physically covered up.

"I'm sure you could put us at ease by covering the cameras. I'm sure you can find some small Singapore Airlines stickers to put on (them)," wrote Twitter user Kate.

For safety and security reasons, most aircraft are equipped with surveillance cameras.

For example, there are cameras outside the cockpit that allow pilots to check the area before they unlock the door for cabin crew members and other staff to enter.

There are also cameras to monitor the rest of the aircraft cabin, if necessary.

There is typically a control switch at the back of the plane that cabin crew can activate to allow pilots to view what is happening.