Google-owned Fitbit has ordered the recall of almost two million smartwatches worldwide after one hundred users reported burn injuries as a result of an overheating battery.

The fitness gadget maker said anyone who bought the $US299 ($411) Iconic smartwatch with the model number FB503 should immediately stop using the product and contact Fitbit for packaging to return it.

According to the US Consumer Product Safety Commission (CPSC), around one million units of the recalled watch were sold in the US, and an additional 693,000 sold overseas.

It is unknown how many of the Ionic smartwatches were sold in Australia.

The US watchdog said on Wednesday the hazard came from the lithium-ion battery within the Ionic watch, which can overheat, posing as a threat to cause burns.

Customers will receive a full refund and a discount of 40 per cent to purchase certain products from the recall, Fitbit said.

The CPSC reported Fitbit received 115 reports of the battery overheating in the US, with 78 reports of burn injuries including two reports of third-degree burns and four claims of second-degree burns.

An additional 59 reports of battery overheating and 40 reports of burn injuries were made internationally.

Tweet from @fitbit

Fitbit, based in San Francisco, introduced the Ionic watches in 2017 and stopped producing them in 2020.

Google completed its $US2.1 billion ($2.9 billion) acquisition of Fitbit last year, which raised concerns about privacy.

A subsidiary of Alphabet, Google makes most of its money by selling ads that rely on information it collects about its billions of users’ interests and whereabouts.

Privacy watchdogs feared it might exploit Fitbit to peer even deeper into people’s lives.

Google entered a series of commitments in Europe and other parts of the world in which it pledged not to use health and fitness data from Fitbit’s 29 million users to sell more ads.

The District of Columbia and three US states sued Google this year for allegedly deceiving consumers – but not specifically via Fitbit products – and invading their privacy by making it nearly impossible for them to stop their location from being tracked.

DC attorney general Karl Racine alleged Google “systematically” deceived consumers about how their locations were tracked and used.

He also said the internet search giant has misled users into believing they could control the information the company collected about them.

– with AAP