Japan's All Nippon Airways (ANA) is asking its passengers to go to the toilet before boarding so it can reduce aircraft weight.

The unusual request is part of an experiment by the airline to cut carbon dioxide emissions.

Japan's NHK television is reporting that ANA began the one-month experiment today on 42 international and domestic flights.

The airline will place staff near boarding gates to ask passengers waiting for flights to go and use the restroom.

ANA hopes it will reduce the weight of the aircraft and cut nearly five tonnes of carbon dioxide emissions from flights.

The airline says it may expand the trial if it is well received by passengers.