Britain launched an investigation into Apple and Google's smartphone operating systems, app stores and browsers on Thursday, its second use of recently bulked up regulatory powers to scrutinise big tech companies.

Fitbit failed to report overheating incidents involving its Ionic watches in which customers suffered serious burns, safety regulator said.

The Consumer Product Safety Commission said Thursday that Fitbit knew a defect in its Ionic smartwatches created an unreasonable risk of serious injury or death, as it had received numerous reports of the devices overheating while being worn and leaving some consumers with second- and third-degree burns.

Fitbit has settled with the U.S. Consumer Product Safety Commission (CPSC) over a longstanding defeat that caused some wearers to sustain burns. The deal finds the Google-owned fitness company paying a $12.