The rules have been brought in across the European Union, as well as in some other European countries and in the United States and Canada.
Under the restrictions, passengers will not be allowed to carry more than 100 ml of liquids, gels or sprays per container. The containers will have to be placed in a transparent one-litre plastic bag, and be able to fit without problems into the bag. The bag must be re-sealable.
Medicines, baby food and food required for a special diet are exempt from the restrictions, and may be carried on board of needed during the flight.
Bottles purchased in airport shops after passing through security controls are also exempt, except on flights to the United States.
The new rules come after British authorities uncovered what they say was a plan to blow up transatlantic airliners using liquid explosives.