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Apple's plans to develop an autonomous electric car entirely in-house appear to have been re-calibrated, after dozens of employees reportedly leave the tech giant's automotive unit.

The staff change suggests that it may take Apple longer to develop an autonomous car. The firm began recruiting for its car division in 2014, although it has never publically acknowledged the move.

Apple is keen to develop new revenue streams in order to reduce reliance on its flagship iPhone product, which has seen sales begin to decline in recent months.

Steve Zadesky left the car team over the summer and has been replaced by Apple veteran Bob Mansfield, who appears to have re-focussed the unit's goals.

In 2014 Apple hired hundreds of people from across the tech and automotive industries. For the last two years these staff have been working in unmarked buildings near the firm's HQ in Cupertino, California.

According to people familiar with the situation, Apple may be re-focussing its efforts on systems that drive an autonomous car, rather than manufacturing the car entirely by itself.

Traditionally Apple has retained full control over all aspects of its products – both hardware and software. The changes could mean that a traditional car maker is brought in to make Apple's car.

Many large companies are investing heavily in self-driving car technology in recent years, which is seen by many as the future of the car industry.