Image copyright Getty Images Image caption Fiat's deal with Google gives the tech company 100 Chrysler Pacifica minivans to add to its driverless fleet

Fiat Chrysler has announced a deal with Google to double the size of the tech giant's fleet of self-driving cars.

Fiat will supply 100 Chrysler Pacifica vans and provide engineers to help integrate the technology.

The companies described the deal as the most advanced partnership to date between Silicon Valley and a traditional carmaker.

Google wants to add more cars to its fleet to increase the amount of road testing it does.

Fiat's chief executive has in the past raised also concerns about the tech industry's impact on the carmakers.

Sergio Marchionne called tech companies moving into the sector "disruptive interlopers" and questioned the calibre of the vehicles they could produce.

"The opportunity to work closely with [Fiat] engineers will accelerate our efforts to develop a fully self-driving car that will make our roads safer," said John Krafcik, Google's head of self-driving cars.

Google has said it believes driverless cars could be ready to goes on sale by 2020.

"Minivans fit into the transportation fleets easily," said Karl Brauer, a senior analyst at Kelley Blue Book. "They can be a box-on-wheels and can move more humans around."

The announcement of the partnership came a week after Astro Teller, the head of 'Moon Shots' at Google said the driverless cars project may soon move from under the umbrella of the Google X division that focuses on futuristic innovations and projects.

Google will own the Fiat cars, and both companies will be free to work with other companies to develop driverless technology.

But the deal could propel Fiat to the head of the self-driving pack and position it to become a major manufacture for Google.