The EU on Friday slapped Google with a massive 2.95 billion euro antitrust fine for favouring its own advertising services, despite US President Donald Trump's warnings not to target US big tech.

Google vowed to appeal the decision by the European Commission, which accused the US firm of distorting competition in the 27-nation bloc.

"Google abused its dominant position in adtech harming publishers, advertisers, and consumers. This behaviour is illegal under EU antitrust rules," EU competition chief Teresa Ribera said.

Trump has threatened to go after Europe for its rules on the digital market and on policing content, which affect tech giants based in the US.

Earlier this week, it emerged the commission had hit pause on the fine, seemingly for fear of US retaliation.

The EU is still waiting for the United States to make good on a promise to lower tariffs on cars under a trade deal agreed in July.

Brussels ordered Google to end its "self-preferencing practices" and take steps to cease its inherent conflicts of interest.

"Google has 60 days to inform the Commission on how it plans to do so," Ribera said.

"If it fails to propose a viable plan, the Commission will not hesitate to impose an appropriate remedy."

She said that, "at this stage, it appears that the only way for Google to end its conflict of interest effectively is with a structural remedy, such as selling some part of its Adtech business".

Google said the commission's decision was "wrong" and it would appeal.

"It imposes an unjustified fine and requires changes that will hurt thousands of European businesses by making it harder for them to make money," said the firm's global head of regulatory affairs, Lee-Anne Mulholland.

"There's nothing anticompetitive in providing services for ad buyers and sellers, and there are more alternatives to our services than ever before." (AFP)