Three whistleblowers have come forward with hundreds of pages of evidence suggesting wrongdoing at the Clinton Foundation, a Republican congressman says.

Mark Meadows, head of the House Oversight Subcommittee, said the documents suggest misappropriation of funds and quid-pro-quo promises made to donors during Hillary's time as secretary of state.

Meadows spoke to Fox News about the documents ahead of an investigative hearing on the Clinton Foundation which is due to take place next week.

Three whistleblowers have handed over hundreds of pages of documents which could indicate misuse of funds and promises made to donors while Hillary was Secretary of State (file image)

The hearing will review evidence collected by U.S. Attorney John Huber, who was tasked with investigating the Foundation by ex-Attorney General Jeff Sessions.

It comes after The Hill reported that 6,000 pages of evidence on the Clinton Foundation was secretly handed to the FBI and IRS last year.

The papers allege that the Foundation engaged in illegal activities and may be liable for millions of dollars in delinquent taxes and penalties.

The documents also showed commingling of personal and Foundation affairs, especially by former President Bill Clinton, according to The Hill.

The evidence was compiled by a firm called MDA Analytics LLC and included a submission by another whistleblower.

A spokesman for the Clinton Foundation said at the time: 'The Clinton Foundation has been one of the most heavily scrutinized charitable organizations in the world, and subjected to outrageous, politically motivated allegations that have been proven false time and time again.

'Critics continue to resurrect these false claims to try to damage the reputation of the Clintons and the Clinton Foundation.

Mark Meadows, head of the House Oversight Subcommittee, spoke out about the documents ahead of a hearing into the Foundation which is due to take place next week

'The fact is, the Clinton Foundation has demonstrably improved the lives of millions of people across America and around the world, while earning top ratings from charity watchdog groups in the process.'

Meadows has previously raised questions about a large drop in funds donated to the Foundation after Hillary lost her 2016 presidential race to Donald Trump.

Donations fell from $63 million in 2016 to $27 million in 2017.

He said: 'The remarkable significance of the drop in Clinton foundation donations raises grave concerns their operations were not above board as the American people have been led to believe.

'Whenever we look at the possibility of 'pay to play' by government officials, current or former, it demands answers--and anyone who uses public office to sell access for their own financial benefit must be held accountable.'

Meadows is a close ally of Donald Trump who has called for investigations into his former Democrat opponent.

The Clinton Foundation defended itself against the allegations, saying the fall in donations was due to the Clinton Global Initiative shutting down.