Google admitted it was blocking several major commercial Australia news outlets including News Corp papers and Guardian Australia from a small number of search users.

Google has started hiding Australian news sites from some local users, in an experiment that comes amid Canberra's push to compel tech firms to pay media outlets for their content.

Canberra plans to force Google and Facebook to pay media organisations when their platforms host their content or face millions of dollars in fines, in one of the most aggressive moves globally to check the power of the US digital giants.

The "world first" rules, due to come into effect this year, will apply to Facebook's "News Feed" and Google searches - and have drawn the tech companies' ire.

On Thursday, Google admitted it was blocking several major commercial news outlets including News Corp papers and Guardian Australia from a small number of search users.

Old links or content from other sites were reportedly appearing instead.

A Google spokesman said the changes were part of the "tens of thousands of experiments" it runs.

We're currently running a few experiments that will each reach about 1 per cent of Google Search users in Australia to measure the impacts of news businesses and Google Search on each other, he said in a statement.

In 2018, the value we provided to publishers through referral traffic alone was estimated at A$218 million, he added.

Google has previously warned the way Aussies use Google is at risk if the law comes into effect, while Facebook has threatened to block users and media organisations in Australia from sharing news stories.

The initiative has been closely watched around the globe, as news media worldwide suffer in an increasingly digital economy where advertising revenue is overwhelmingly captured by big tech firms.

The experiments were due to finish by early February, the Google spokesman said.