Two Joint Strike Fighter planes, worth around $100 million each, have been forced to stay an extra day at the Avalon Air Show west of Melbourne because there could be lightning near their next destination.

The aircraft were scheduled to fly to Amberley, south-west of Brisbane yesterday, but will now leave today instead.

The F-35s were one of the main drawcards at the air show, which was attended by the US-led program developing the planes.

But the aircraft will require modifications before they can fly in lightning — a process that will be completed on Australia's fleet of F-35s before delivery next year.

The AU-1 and AU-2 aircraft were the first two Australian F-35s to roll off the Lockheed Martin assembly line in Fort Worth, Texas, in July 2014.

In December that year, both aircraft were flown to Luke Air Force Base in Arizona to join an international pilot training pool.

The Australian Government approved the purchase of 14 F-35A fighters in November 2009, and a second tranche of 58 aircraft in April 2014, equipping three squadrons, with the first expected to be delivered to Australia in 2018 and enter service in 2020.

A further tranche of 28 aircraft, bringing the total up to 100 aircraft for a fourth squadron, has yet to be decided on.