Jimmy Fallon has apologised for wearing ''blackface'' during a 'Saturday Night Live' skit two decades ago.

The 45-year-old talk show host - who was a regular fixture on the weekly entertainment show from 1998 until 2004 - has responded to backlash over the ''unquestionably offensive'' sketch from 2000 which has resurfaced this week and showed him doing an impression of comedian Chris Rock.

Jimmy tweeted: ''in 2000, while on SNL, I made a terrible decision to an impersonation of Chris Rock while in blackface. There is no excuse for this.

''I am very sorry for making this unquestionably offensive decision and thank all of you for holding me accountable.''

In the controversial skit, Jimmy - who was joined by Darrell Hammond playing Regis Philbin - stepped out in blackface as he made some jokes in the style of the comedian.

Social media users had demanded an apology from the 'Tonight Show' star, and the clip - which doesn't appear on the 'SNL' website or YouTube channels - was circulated on Twitter with the hashtag ''#JImmyFallonIsOverParty''.

Chris is yet to comment publicly on the incident.

In 2018, NBC - which broadcasts both programmes - parted ways with Megyn Kelly after she defended blackface in a controversial Halloween themed segment.

She said at the time: ''Truly, you do get in trouble if you are a white person who puts on blackface for Halloween, or a black person who put on whiteface for Halloween.

''When I was a kid, that was OK as long as you were dressing up as a character.''

The anchor - whose own 'Megyn Kelly Today' show was removed from NBC's schedule - apologise for her comments.

She said: ''I want to begin with two words: 'I'm sorry'. I defended the idea [of blackface] saying as long as it was 'respectful' and part of a Halloween costume it seemed OK. Well I was wrong and I am sorry.''