Teen climate activist Greta Thunberg is staring down at pedestrians in the heart of San Francisco where an artist is painting a mural of the Nobel Peace Prize nominee.

Key points: The artist who is painting the giant mural is doing it for free

The artist who is painting the giant mural is doing it for free It is to be one of a series of artworks commissioned to honour climate change activists

It is to be one of a series of artworks commissioned to honour climate change activists Ms Thunberg is currently travelling around North America to raise awareness of climate change

Argentine muralist Andres Iglesias, who signs his art with the pseudonym Cobre, is set to finish the artwork of the Swedish 16-year-old in the city's Union Square by next week.

Cobre told news site SFGate that he was donating his time to complete the work and that he hoped the mural would help people realise "we have to take care of the world".

Cobre said he was searching for a building for a new mural when environmental not for profit One Atmosphere approached him about the project.

Executive director Paul Scott said he believed Cobre was the perfect choice to create the first of what the organisation hopes will be a series of works honouring climate change activists.

Ms Thunberg herself had spent the day at a climate change rally in Charlotte, North Carolina, and shut down a heckler who tried to disrupt her speech.

"I think if you want to speak with me personally, maybe you can do it later," Ms Thunberg said before the crowd erupted, chanting her first name.

The 16-year-old, who has been travelling around North America to raise awareness about climate change, was imploring fellow youth leaders to speak out in the fight against global warming when she paused as someone near the stage tried to speak over her.

"It can be hard in times like these to find hope, I can tell you," Ms Thunberg said.

"And I can tell you I have not found much hope in politicians and corporations. It is the people who are now our greatest source of hope.

"While we young people may not be able to vote or make decisions today, we have something just as powerful," she said. "And that is our voices. And we need to use them."

As she had in previous speeches, Ms Thunberg chastised adults for their inaction on fighting climate change.

"It is we young people who are the future," she continued.

"There is not enough time to wait for us to grow up and become the ones in charge because we need to tackle the climate and ecological emergency right now.

"If the adults and people in power are too immature to realise that, then we need to let them know."

AP