SAN FRANCISCO, Sept. 16 (Xinhua) -- The U.S. National Highway Traffic Safety Administration has launched an investigation into complaints that door handles on Tesla's Model Y SUVs can become inoperable under certain conditions, local media reported Tuesday.

The agency's Office of Defects Investigation (ODI) said it has received nine reports from owners who were unable to enter their vehicles. In the most common scenario, parents reported being locked out after exiting the car, unable to open the rear doors to retrieve their children. In four cases, owners broke a window to regain access, according to ODI.

A preliminary review found the problem may occur if the electronic door locks do not receive enough voltage from the vehicle's battery system. ODI noted that none of the reports indicated low-voltage battery warnings were displayed.

The report said that Tesla vehicles are equipped with manual door releases inside, though these may be difficult for children to reach and some owners are unaware of their presence.

According to Tesla's owner manuals, restoring power to the electronic locks requires a multi-step process using an external power source.