A "suspicious device" found attached to the bottom of a car in Brisbane's Fortitude Valley has turned out to be harmless.

Queensland Police were called to Arthur Street about 7:40am and declared an emergency situation a short time later.

No nearby residents were evacuated, but motorists were asked to avoid the area.

Acting Inspector Gregory Veivers said the device did not look like a bomb, but more like a GPS device, less than 30 centimetres big.

He said it is unclear why someone would attach the device to the car.

"It was pretty basic, slightly elaborate, but basic," he said.

"The vehicle is safe.

"A device has been located, it is harmless and will be the subject of further examination by our scientific team and detectives.

"Those investigations are ongoing."

There are no suspects at this stage.