(Reuters) - Amazon.com's ( AMZN ) self-driving car unit Zoox said on Wednesday it plans to start testing its robotaxis in Austin and Miami, a move that will mark its first trial sites outside the western United States.

Zoox will deploy its retrofitted Toyota Highlander test fleet in small areas near the business and entertainment districts of the two cities, it said in a statement.

The announcement comes amid an investigation by the National Highway Traffic Safety Administration (NHTSA) into 500 Zoox vehicles equipped with automated driving systems after two crashes.

Austin and Miami will mark the fourth and fifth public testing locations for Zoox, having already established operations in San Francisco, Las Vegas and Seattle.

Zoox said it will not offer public rides in Austin and Miami yet but is exploring several cities for commercial offerings after its initial launch in its target markets of Las Vegas and San Francisco.

Along with Zoox, self-driving robotaxi companies like General Motors' ( GM ) Cruise and Alphabet's Waymo have been embroiled in investigations by the NHTSA involving the performance of autonomous driving cars.

Cruise said on Monday it has resumed operations in Dallas, Texas, with a small fleet of human drivers after it paused operations due to an incident in San Francisco involving one of its robotaxis in October last year.