Teenage climate activist Greta Thunberg has taken aim at Donald Trump in a tongue-in-cheek jibe on social media, after the US President said her selection as Time's Person of the Year was "so ridiculous".

Key points: US President Donald Trump tweeted that Greta Thunberg needed to "chill"

US President Donald Trump tweeted that Greta Thunberg needed to "chill" Mr Trump is the second world leader to take aim at Ms Thunberg this week after Brazil's President called her a "brat"

Mr Trump is the second world leader to take aim at Ms Thunberg this week after Brazil's President called her a "brat" Ms Thunberg responded by mocking Mr Trump's comments in her Twitter biography

Ms Thunberg won the magazine's annual honorific on Wednesday, for her work inspiring millions of young people to take action against climate change.

The Swedish teenager has become a symbol of a growing movement of young climate activists after leading weekly school strikes in her country that inspired similar actions in about 100 cities worldwide.

While many took to social media to congratulate Ms Thunberg on the decision, it drew the ire of Mr Trump, who labelled the announcement "so ridiculous".

"Greta must work on her Anger Management problem, then go to a good old-fashioned movie with a friend! Chill Greta, Chill!" Mr Trump wrote on Twitter.

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Ms Thunberg fired back on Twitter by updating her biography to read: "A teenager working on her anger management problem. Currently chilling and watching a good old-fashioned movie with a friend."

She has been outspoken about her diagnosis with Asperger's syndrome, an autism spectrum disorder associated with high intelligence and impaired social skills.

Greta Thunberg's updated Twitter bio, changed after Donald Trump's tweet. ( Twitter: @GretaThunberg )

"I have Aspergers and that means I'm sometimes a bit different from the norm," she tweeted this year.

"And — given the right circumstances — being different is a superpower."

Trump and Thunberg had previous run-in

The spat, which propelled Ms Thunberg to trend on Twitter with several hashtags, came on the fourth anniversary of the Paris climate pact that Mr Trump withdrew from soon after taking office.

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It's not the first time the Republican President has targeted Ms Thunberg.

In September, Mr Trump retweeted a clip of the teenager's speech to a United Nations climate summit in which she angrily denounced world leaders for failing to tackle climate change by demanding: "How dare you?"

Brazil's President Jair Bolsonaro called Ms Thunberg a brat using the Portuguese word "pirralha." ( AP: Andrea Comas )

Mr Trump quipped that she seemed like a "very happy young girl looking forward to a bright and wonderful future. So nice to see!"

Ms Thunberg also changed her Twitter biography following that slight to describe herself as: "A very happy young girl looking forward to a bright and wonderful future."

Brazil's leader takes aim at 'brat'

Mr Trump is the second world leader to take aim at Ms Thunberg this week.

Her concern over the slayings of indigenous Brazilians in the Amazon drew a harsh rebuke from Brazil's President on Tuesday.

"Greta said that the Indians died because they were defending the Amazon," Jair Bolsonaro said.

"It's impressive that the press is giving space to a brat like that," he added, using the Portuguese word "pirralha."

Ms Thunberg responded by changing her bio on Twitter, where she has over 3 million followers, to say "Pirralha."

AP/Reuters