The US Air Force has temporarily grounded dozens of F-35 stealth fighters while it investigates an oxygen supply issue aboard the expensive planes, officials said today.

The 56th Fighter Wing of Luke Air Force Base, Arizona "will continue their pause in local F-35A flying to coordinate analysis and communication between pilots, maintainers, medical professionals and a team of military and industry experts," spokeswoman Major Rebecca Heyse said in a statement.

The planes were grounded on Friday due to five incidents since May 2 in which pilots experienced hypoxia-like symptoms.

Currently, the Wing has 55 F-35A planes that are used to train pilots from the US and other air forces that are buying the jet.

Heyse said it was unclear when the "pause" would be lifted, but noted that none of the incidents were serious and pilots were able to use their training to avert any problems.

"The safety of our airmen is paramount and we will take as much time as necessary to ensure their safety," she said.

Another spokesman, Captain Mark Graff, said in a statement that a backup oxygen system kicked in as designed.

The F-35 comes in three versions, with the "A" model being that of the Air Force.