Democratic candidate Hillary Clinton has labelled her Republican rival Donald Trump a “racist” and a “liar” during their first presidential debate on Monday night (US time).

Mr Trump interrupted the Democratic candidate constantly throughout the event, while Ms Clinton generally maintained her composure.

Mr Trump, who frequently interrupted NBC moderator Lester Holt throughout the broadcast, constantly referred to his opponent as “her” and “she” rather than the more formal “Secretary Clinton”.

But despite a sustained barrage of from the Republican throughout the first half of the debate, it wasn’t until the topic of race relations was raised that Ms Clinton displayed some aggression, calling Trump a “racist” and a “liar”.

‘Long record of racist behaviour’

The acrimony began with a question from African American moderator Lester Holt referring to Mr Trump’s claims that President Obama was not born in the United States, and therefore not eligible to be president.

“Mr Trump, for five years you perpetuated a false claim of the nation’s first black President wasn’t a natural born citizen,” Mr Holt said.

Interrupting Mr Holt, the Republican candidate offered up a confusing, longwinded explanation attempting to implicate Ms Clinton’s ex-campaign manager as the true culprit. He then declared he was “proud” that he had forced Mr Obama to produce his birth certificate in 2011.

Presidential debate: Clinton slams Trump over ‘racist birther lie’ #debates #debates2016 https://t.co/fcJkmnL3mL

— Globalnews.ca (@globalnews) September 27, 2016

Hilary Clinton jumped at the chance to admonish Mr Trump over over the claims, adding that Mr Trump had been sued multiple times for refusing to allow African Americans into his company’s rental properties.

“He has really started his political activity based on this racist lie,” the Democratic candidate argued.

“So he has a long record of engaging in racist behaviour,” she said. 

Trump’s body language and tone of voice was significantly more aggressive. Photo: Getty

Trump plugs new business mid-debate

Mr Trump, who declared his “temperament” to be his winning trait at one point in the debate, was criticised by some viewers for using the platform to spruik his new hotel.

“We are just opening up on Pennsylvania Avenue right next to the White House.

“If I don’t get there one way, I will get to Pennsylvania Avenue another. But we are opening the old post office … under budget, ahead of schedule.”

Viewers thoroughly enjoyed the “advertisement”, with many questioning its place in a presidential debate.

Nice ad for a Trump hotel in the middle of a PRESIDENTIAL DEBATE

— Tim Dowling (@IAmTimDowling) September 27, 2016

Trump’s missing tax returns

Ms Clinton pushed the Republican candidate on his refusal to release his tax return – a tradition upheld by presidential candidates throughout history.

“Maybe he’s not as rich as he says he is,” she said. “Maybe he’s not as charitable as he pretends to be … we’ve been told through investigative reporting that he owes $650 million to Wall Street and foreign banks.”

Mr Trump responded by telling Ms Clinton he would release the information if the Secretary of State released information from her private email server.

https://twitter.com/drewharwell/status/780580953429344256