Prison guards assigned to monitor Jeffrey Epstein on the night he apparently killed himself fell asleep and failed to check on him for three hours before falsifying records to cover up their neglect, according to officials.

The two guards have been placed on leave and the warden of New York City’s Metropolitan Correctional Centre (MCC) has been reassigned as federal authorities investigate the financier’s death, the Justice Department has announced.

It comes amid mounting evidence of failures at the chronically understaffed prison which allowed the 66-year-old to take his own life as he awaited trial on charges of sexually abusing teenage girls.

Epstein, who had attempted to take his own life in July, was taken off a suicide watch last month for reasons that have not been explained and should have been checked on by a guard every 30 minutes.

Investigators have learned those checks were not done for three hours before he was found hanged at 6.30am on Saturday, according to a person familiar with the case.

Guards at the jail in Manhattan are suspected of falsifying log entries to incorrectly show they had been visiting Epstein’s cell during the gap.

Surveillance video reviewed after his death showed they did not make some of the checks noted in the records, a source told Associated Press.

Both guards assigned to watch Epstein and other prisoners were asleep during some or all of the three hours he went without checks, reported The New York Times, which cited unnamed law enforcement and prison officials.

One of the guards was not a regular prison officer and had been drafted in because of staffing shortages, according to Serene Gregg, president of the local branch of the American Federation of Government Employees.

A second inmate who had been assigned to share a cell with Epstein had been transferred elsewhere the day before his death and was not replaced.

Attorney general William Barr said on Monday he was "frankly angry to learn of the MCC's failure to adequately secure this prisoner".

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"We will get to the bottom of what happened and there will be accountability,” he added.

The FBI and the Justice Department's inspector general are both probing Epstein's death and US president Donald Trump has said he wants a "full investigation" into what happened.

Jeffrey Epstein was found dead in his cell at the Metropolitan Correctional Centre in Manhattan, New York City (AP)

Epstein was being held without bail as he awaited trial on federal sex trafficking and conspiracy charges that could have led to him being jailed for 45 years.

Federal prosecutors in New York are pursuing a parallel investigation into whether any associates of Epstein should be charged with assisting him in what authorities say was his rampant sexual abuse of teenage girls.

Mr Barr warned that any co-conspirator in the sex crimes case against Epstein "should not rest easy". He added: "The victims deserve justice, and they will get it."

Epstein, who once counted Mr Trump and former president Bill Clinton as friends, was arrested on 6 July and pleaded not guilty to charges of sex trafficking involving dozens of girls as young as 14.