Invercargill resident Raewyn Stiles was unable to get in to her car because of interfering radio frequencies.

A radio frequency has been interfering with car remote keys in Invercargill, leaving drivers stranded in the central business district this week.

Raewyn Stiles said her husband told her that he struggled to unlock the car and the car remote was not working properly on Thursday.

She went to get replacement batteries for the remote and when she returned to her car, parked on Dee St, the remote would not unlock the car.

John Hawkins/Stuff Robbie Baxter Autos service manager Kris Milne says dozens of car owners had come into the car sales business reporting that their car remotes were not working.

She then called AA Roadside Assistance for help.

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The man who assisted remarked to her that it was the third callout that day to a Hyundai with a malfunctioning car remote, she said.

Ben Bootsma/Stuff Invercargill resident Raewyn Stiles was unable to get in to her car on Thursday because of interfering radio frequencies.

Robbie Baxter Autos service manager Kris Milne said about a dozen car owners turned up to the dealership on Monday reporting that their car remotes had been malfunctioning.

Car owners had said they were unable to lock or unlock their cars and some were even unable to start the vehicles with their car remotes, Milne said.

When staff inspected the remotes they found no issues and they could not find any faults with the cars that were brought to the dealership.

On Tuesday, more people turned up to report problems and staff became suspicious that something was wrong.

After speaking to another dealership in town, they found out that the remotes were not unlocking the cars because the signals they sent had been blocked by a stronger signal being transmitted in the CBD, Milne said.

GWD Motor Group parts manager Phil Ramsay said there was a noticeable spike in of people coming into the dealership to replace the batteries in their car remotes.

Ministry of Business, Innovation and Employment's Radio Spectrum Management (RSM) compliance manager Fadia Mudafar said it was contacted by Invercargill Police who said there was a significant number of people getting replacement batteries for car remotes because they were not working.

An RSM Compliance Officer provided advice to police on what frequency it was likely to be and a police technician tracked it to a legitimate repeater on top of the Menzies Building.

A search of the radio frequency license register shows amateur radio operator Daniel Erickson holds the licence on behalf of amateurs to transmit on 434.050MHz.

Mudafar said amateurs have primary use of the frequency range 433.050 to 434.920MHz.

"Remote controls, such as those in car door remotes, operate within the Short Range Device Notice and have secondary use of the same frequency range 433.050 to 434.920MHz."

Both parties are legally allowed to transmit on the frequency.

The repeater is currently off while the license holder works with RSM to find a solution, Mudafar said.

"RSM has seen similar issues on shared frequencies before, but not with amateur transmissions."