US President Donald Trump on Monday sought to sue multinational technology company Google for allegedly manipulating up to "16 million votes" in favour of Democratic presidential candidate Hillary Clinton in the 2016 elections.

The election results had surprised many as Clinton was tipped to win by the media and pollsters.

"Wow, Report Just Out! Google manipulated from 2.6 million to 16 million votes for Hillary Clinton in 2016 Election! This was put out by a Clinton supporter, not a Trump Supporter! Google should be sued," Trump tweeted.

"My victory was even bigger than thought!" he said.

Trump was apparently referring to the work of Robert Epstein, a researcher with the California-based American Institute for Behavioral Research and Technology.

Epstein had testified in a Senate hearing in June that his research shows Google's search results pushed at least 2.6 million people to vote for Clinton in 2016.

Google CEO Sundar Pichai was asked about Epstein's work last year when he testified before a House panel and said the company had investigated it and pointed to issues with the study's methodology.

In a statement on Monday, a Google spokesperson called Epstein's claim "debunked", pointing out it has been circulating for three years.

"This researcher's inaccurate claim has been debunked since it was made in 2016," the spokesperson said.

"As we stated then, we have never re-ranked or altered search results to manipulate political sentiment. Our goal is to always provide people with access to high quality, relevant information for their queries, without regard to political viewpoint," the spokesperson said.

In 2017, Google dismissed Epstein's research as "nothing more than a poorly constructed conspiracy theory".