The world's first driverless taxis went into operation on Thursday in Singapore in a limited public trial, beating giants like Uber in the race to roll out the revolutionary technology.

The "robo-taxi service" is being tested at a small research campus well away from the thrum of the Asian business hub.

Data from the experiment will feed into the roll-out of driverless taxis across the city-state in 2018, said nuTonomy, a US-based tech start-up that developed the software used in the vehicles.

"The trial represents an extraordinary opportunity to collect feedback from riders in a real-world setting," said nuTonomy chief executive and co-founder Karl Iagnemma.

"This feedback will give nuTonomy a unique advantage as we work toward deployment of a self-driving vehicle fleet in 2018," he said.

The six taxis -- Renault Zoe and Mitsubishi i-MiEV electric vehicles -- will operate in a 2.5 square mile (4.0 square kilometre) area, with set pick-up and drop-off points. Trips have to be booked through the company's smartphone app.

Although the high-tech cars will drive themselves, each journey will be accompanied by a nuTonomy engineer, who will observe how the machine performs, and be ready to take over in the event of a problem, the company said.

Ride-sharing giant Uber said last week that it would be launching driverless cars in the US city of Pittsburgh by the end of August. It has also established a $300 million venture with Chinese-owned, Swedish-based Volvo to develop self-driving cars for sale by 2021.

Separately, Google parent Alphabet announced in May that it is partnering Fiat Chrysler in expanding its fleet of self-driving vehicles, which it hopes will hit the road by end-2016.

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