Japan's top car maker Toyota is investing $US1 billion ($A1.3 billion) in Grab, the leading ride-hailing company in Southeast Asia.

Toyota said on Wednesday it had reached a deal with Grab Holdings to strengthen a partnership they already had to grow mobility services in the region.

A Toyota executive will be appointed to Grab's board and another Toyota personnel is being tapped to be an executive officer at Grab, the company said.

Grab, which is similar in its services to Uber in the US, is in eight nations in the region, including Malaysia, Singapore and Indonesia.

Toyota was initially cautious about ride-sharing and autonomous-driving technology.

In recent years the maker of the Camry sedan, Prius hybrid and Lexus luxury models has been aggressively playing catch-up, signing on partners around the world.