A police publicity exercise has inadvertently triggered fears of an unfolding mid-air emergency, after Adelaide locals spotted a plane and a helicopter flying close together over the city.

Key points: Onlookers were alarmed to see a plane flying close to a helicopter over Adelaide

Onlookers were alarmed to see a plane flying close to a helicopter over Adelaide Some said the chopper appeared to be chasing the plane as the aircraft circled the city

Some said the chopper appeared to be chasing the plane as the aircraft circled the city Police later clarified the exercise was for a photo shoot to gather publicity material

The aircraft were seen circling Adelaide on Wednesday morning, apparently only dozens of metres apart, with many onlookers casting their eyes skywards.

A flight tracking map posted online shows the two aircraft both left Adelaide Airport before doing several laps around the CBD and inner suburbs, but there were also sightings further afield.

"Did anyone in Adelaide just see a plane circling the city, being chased by a helicopter?" one person wrote on social media.

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ABC Radio Adelaide also received text messages from concerned listeners who wanted an explanation.

"There's a helicopter chasing a small plane over the city. Is this normal?" one texted in.

One witness said it looked as if the helicopter was chaperoning the plane. ( ABC News: Angelique Donnellan )

Another listener suggested the plane appeared to be tethered to the helicopter.

"We have called the Adelaide Airport, we have called Airservices Australia and we have called [SA Police] but no-one seems to have any information about it," ABC Radio Adelaide presenter Sonya Feldhoff told listeners.

ABC reporter Angelique Donnellan witnessed the plane and the helicopter on Wednesday morning at Grange.

"It was very eye-catching. I thought it was peculiar, they looked really close," she said.

"It crossed my mind: what was going on? I'd never seen anything like this before.

"It looked like the helicopter was chaperoning the plane. I thought maybe it was a private jet, and there was someone important onboard."

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Police have since reassured the public the plane was a police aircraft taking part in a photo shoot.

"A photo shoot featuring the recently refurbished South Australia Police Pilatus PC12 aircraft took place over Adelaide today," police said.

In a statement released several hours after the plane was first spotted, police said the aerial photographs "feature the aircraft's new livery and will be used in corporate publications".

"The aircraft, owned by [SA Police] and used to convey police and prisoners across the state, was refurbished as a part of the scheduled maintenance," police said.

"The flight took place as part of normal operations and no additional costs were incurred."