Tom Hanks perfected his deadpan delivery playing debate moderator Chris Wallace during a Saturday Night Live sketch spoofing the final US presidential debate.

The actor both looked and spoke the part of the Fox News host, introducing the piece by saying: "Tonight is going to be a lot like the third Lord of the Rings movie.

"You don't really want to watch but, hey, you've come this far."

He introduced Kate McKinnon's Hillary Clinton and Alec Baldwin's Donald Trump, who have both nailed their impressions over a series of spot-on debate sketches.

Baldwin opened his powerhouse performance by saying "I'm going to start this debate in the quietest voice possible. In the past I have been as big and loud but tonight I am a sweet little Baby Trump," but it wasn't long till he has yelling, pulling faces and making typically pointed hand gestures.

When he mentioned "bad hombres", McKinnon's Hillary shouted excitedly "I got bingo" and pulled out a Trump Bingo card, which "bad hombres", "racists", "Miss Piggy", "they're all living in hell", and "if she wasn't my daughter".

The sketch ripped on Trump's most memorable moments during the final debate, including his immigration policies, attitude to women's reproductive rights and rambling incoherent answer about ISIS.

He also goes on a rant about how the election is rigged, saying: "Frankly this whole thing is rigged. The newscasters are making me look so bad."

When Hanks' Wallace asks him how this is the case, he replies: "By taking all of the things I say and all of the things I do, and putting them on TV."

Baldwin's incredible impression also nailed Trump's incessant sniffling and frequent heckling of Clinton with "wrong", "liar" and "such a nasty woman".

When Baldwin's Trump said the famous line "Nobody has more respect for women than I do", the sketch cut to clips of huge crowds of people laughing, with Hanks' Wallace saying "Ok, settle down entire planet".

One of the funniest moments came when Trump was boasting about his high-profile supporters, including Sarah Palin and "the best Baldwin brother, Stephen Baldwin."

McKinnon also took a dig at Clinton's expert pivoting from questions about the Wikileaks email controversy and her coached answer about her 30-years experience compared to Trump's.