The Dutch maker of TomTom satellite-navigation units says a "leap year bug" has caused a fault resulting in some of the devices malfunctioning.

The company said a problem with its Global Positioning System firmware -- code embedded in the devices' hardware -- was causing "a limited number of models" to fail to determine their location.

The issue first emerged March 31, the company said, when users were presented with a gray screen and an error message that the device was without a GPS signal.

TomTom told the BBC it would "update customers on which models are affected as soon as we know more."

TomTom users in Britain, Australia, Switzerland and Denmark have said they are having problems.

The company suggested users reset their devices by holding the power button down for 20 seconds, saying the action could result in a temporary fix.

"Please accept our sincere apologies for the inconvenience caused," TomTom said in a statement.