US internet giant Google, whose Android mobile operating system powers most of the world's smartphones, said it was beginning to cut ties with China's Huawei, which Washington considers a national security threat.

The move could have dramatic implications for Huawei smartphone users, as the telecoms giant will no longer have access to Google's proprietary services — which include the Gmail and Google Maps apps — a source close to the matter told AFP.

In the midst of a trade war with Beijing, President Donald Trump has barred US companies from engaging in telecommunications trade with foreign companies said to threaten American national security.

Read: US intelligence says Huawei funded by Chinese state security: report

The measure targets Huawei, the world's second-biggest smartphone maker, which has been listed by the US Commerce Department among firms that American companies can only engage with in trade after obtaining the green light from the authorities.

The ban includes technology sharing.

"We are complying with the order and reviewing the implications," a Google spokesperson told AFP.

"For users of our services, Google Play and the security protections from Google Play Protect will continue to function on existing Huawei devices."

Google, like all tech companies, collaborates directly with smartphone makers to ensure its systems are compatible with their devices.

Due to the ban, Google will now have to halt business activities with Huawei that involve direct transfer of hardware, software and technical services that are not publicly available — meaning Huawei will only be able to use the open source version of Android, the source told AFP.

Google apps such as Gmail and Maps should remain functional on Huawei phones at least initially, another source told AFP.

But while the ban on technology sharing is in place, Huawei will be required to manually access any updates or software patches from Android Open Source Project — the code accessible to all outside programmers — and also to distribute the updates to users itself.

A person familiar with the matter who requested anonymity told Bloomberg News that Huawei will be unable to offer Google's proprietary apps and services in the future.

Huawei did not immediately respond to requests for comment.

5G leader

Huawei is a rapidly expanding leader in 5G technology, and its smartphones outsold Apple's iPhones in the first quarter of this year, seizing the California company's second-place spot in a tightening smartphone market dominated by Samsung.

Read: Huawei jumps ahead of Apple in tough smartphone market

But the Chinese firm remains dependent on foreign suppliers.

It buys about $67 billion worth of components each year, including about $11 billion from US suppliers, according to The Nikkei business daily.

Huawei is the target of an intense campaign by Washington, which has been trying to persuade allies not to allow China a role in building next-generation 5G mobile networks.

US government agencies are already banned from buying equipment from Huawei.

Huawei founder and CEO Ren Zhengfei said on Saturday that "We have not done anything which violates the law," adding the US measures would have a limited impact.

Ren's army background and Huawei's opaque culture have fueled suspicions in some countries that the firm has links with the Chinese military and intelligence services.