Climate activist Greta Thunberg has been charged with disobeying police during a June climate protest in southern Sweden, the public prosecutor said Wednesday, most likely risking a fine.

The prosecutor said it had charged the 20-year-old activist after she "refused to obey police orders to leave the site" of a protest in the southern city of Malmo on June 19.

Thunberg joined the protest organised by environmental activist group "Ta tillbaka framtiden" (Reclaim the Future) as they attempted to block the entrance and exit to the Malmo harbour to protest the use of fossil fuel.

"We choose to not be bystanders, and instead physically stop the fossil fuel infrastructure. We are reclaiming the future," Thunberg said in an Instagram post at the time.

On Wednesday, the group said: "After blocking the activities that are burning our future, we are now being charged with criminal offences.

"While charges are being brought against us, the real crime is going on inside the doors we have blocked".

The charge can at most lead to a six-month jail sentence, but prosecutor Charlotte Ottesen told the Sydsvenskan newspaper it normally results in a fine.

A hearing at the Malmo district court has been scheduled for the end of July, the newspaper said.

Greta Thunberg was just 15 when she began her "School Strike for the Climate" in front of Sweden's parliament in Stockholm.

She and a small group of youths founded the Fridays for Future movement, which quickly became a global phenomenon.

In addition to her climate strikes, the young activist regularly lambasts governments and politicians for not properly addressing climate issues.

At the end of March, she condemned what she called an "unprecedented betrayal" from leaders after the publication of the latest report by the IPCC, the UN's climate advisory panel.