John Oliver has delivered a scathing attack on US President-elect Donald Trump, saying his rhetoric was like "reading the to-do list on Satan's refrigerator".

The British comedian tried to make sense of the divisive Republican's astonishing election defeat of Democrat Hillary Clinton in the year's final episode of Last Week Tonight.

"It's true. That happened," Oliver said on the show, adding, "America proved no grandpa is too racist to become the leader of the free world."

A highly-animated Oliver said he would accept the result, but wanted two questions answered.

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"Many people are happy to see him (Trump) in office. Some are voters who think he'll bring jobs back and shake up Washington. Others are happy simply because he isn't Hillary Clinton. And others, of course, are Vladimir Putin and Scott Baio," Oliver said.

"But for the rest of us, we are faced with the same questions as a guy who woke up the day after a Vegas bachelor party, deep in the desert, naked, tied to a cactus and a dead clown. Namely, how the f**k did we get here, and what the f**k do we do now? Donald Trump will be president, and respecting democracy means accepting that. Although there is one sentiment that I would argue takes that a little too far."

On the question of "how did we get here?" Oliver said: "Well clearly there are many possible answers to that question, including misleading forecasts that bred complacency, a flawed candidate who failed to appeal to white, rural, and working class voters, and - and this is worth repeating - deep racism and/or indifference to it. For those, including us, who were shocked by Tuesday, we're going to be examining all of this for years.

"But for tonight, let's look at just one narrow element that may have helped bring us here, because it will be important going forward, and that is our media. Specifically how a system that is supposed to catch a serial liar failed."

The TV host took issue with news pundits calling for the public to give the billionaire businessman a chance.

"Optimism is nice, if you can swing it. But you've got to be careful, because it can feed into the normalisation of Donald Trump. Because he is not normal. He is abnormal," Oliver said.

"He's a human, 'what is wrong with this picture?' He sticks out like a sore thumb, and frankly he even looks like a sore thumb. So giving him a chance in the sense of not speaking out immediately against the policies he's proposed is dangerous. Because some of them are alarming."

He also dissuaded Americans say they're going to move to Canada to avoid living under a Trump presidency.

"For the last eight years, we've had a president we could assume would generally stand up for the rights of all Americans. But that is going to change now. So we're going to have to actively stand up for one another," he said.

"And it can't just be sounding off on the internet or sharing think pieces or videos like this one that echo around your bubble. I'm talking about actual sacrifice to support people who are now under threat."