All models of Onewheel electric skateboards are being recalled after the maker Future Motion received reports of four deaths of users between 2019 and 2021 and multiple reports of serious injuries.

In the recall notice for 300,000 of the self-balancing skateboards, the US Consumer Product Safety Commission warned people to immediately stop using the skateboards, which can stop balancing the rider if the boards limits are exceeded, posing a crash hazard that can result in serious injury or death.

The deaths resulted from head trauma, and in at least three of those cases, the rider was not wearing a helmet, the agency said. The injuries linked to the skateboards included traumatic brain injury, concussion, paralysis, body fractures and ligament damage.

Santa Cruz-based Future Motion initially refused to agree to a recall in November, when the Consumer Product Safety Commission first warned customers to stop using the skateboards.

The agency said it evaluated the Onewheel products and found that they can cause the rider to be ejected from the product, which can result in serious injury or death to the rider.

Future Motion is now cooperating with the recall, and the company is rolling out a firmware update to address the safety issues, using what it called haptic buzz.

Haptic buzz is an alert riders can hear and feel when experiencing certain situations that can result in a crash, Future Motion wrote in its recall statement.

The firmware update will roll out in a few weeks, and is only available for Onewheel GT, Pint X, Pint, and XR products, not original Onewheel and Onewheel+ skateboards, the company said.

Future Motion and the US Consumer Product Safety Commission encouraged riders to wear personal safety equipment. CNN has reached out to Future Motion for comment.