Alphabet’s Waymo unit will begin test drives of its robotaxis in Denver and Seattle this week, with humans behind the wheel, the company said on Tuesday.

“We will begin driving manually before validating our technology and operations for fully autonomous services in the future,” a company spokesperson said in an email. Waymo announced the tests in blog posts.

The autonomous vehicle venture aims to expand its driverless, ride-hailing service across the U.S. after already launching commercial operations in Austin, Texas, as well as Atlanta, San Francisco, Phoenix and Los Angeles.

In some markets, including Austin and Atlanta, Waymo’s driverless rides can only be hailed through the Uber app. In others, riders must use the company’s standalone Waymo One app to book a robotaxi.

Safety drivers, who are employees of Waymo, will man the steering and braking behind the test vehicles in Denver and Seattle. The company is also running similar tests with its robotaxis in New York, having recently obtained permits in the biggest U.S. market.

The company’s test fleet in Denver and in Seattle will include a mix of their fully electric Jaguar iPace and Geely Zeekr AVs.

Waymo told CNBC that it will have up to a dozen cars each in Denver and Seattle to start testing.

Waymo’s primary competition on the global stage is Baidu-owned Apollo Go in China, which operates driverless ride-hailing services throughout Asia. Meanwhile, Tesla has obtained a permit to operate a ride-hailing business in Texas, and is testing a manned robotaxi service in Austin and another in San Francisco.

WATCH: Waymo testing cars with human drivers in New York