A second person has died after a car slammed into a tree near a shopping complex in Adelaide.

An elderly couple were travelling in a Volkswagen when it crashed on the Anzac Hwy near Grassmere St in Kurralta Park just before 1pm on Thursday.

The passenger, an 80-year-old woman, died at the scene.

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Police confirmed that the 81-year-old male driver, who was taken to hospital in a critical condition after the crash, died in the early hours of Friday morning.

It is believed the driver suffered a medical episode, lost control and veered off the road.

Witnesses who ran to help found the driver and his wife in cardiac arrest.

The crash happened near the Kurralta Park Village Shopping Centre in front of dozens of people, including children.

“Seeing young kids being subjected to ... you don’t want them to really know that’s what’s going on,” witness Felicia River told 7NEWS.

The couples’ house is just a few minutes drive from where they crashed.

Neighbours who came to the scene told 7NEWS the pair would often go to the shops together.

The Anzac Hwy was closed to citybound traffic while police examined the scene.

Anyone who witnessed the collision or has any dashcam footage is urged to contact Crime Stoppers.