Swedish climate activist Greta Thunberg will face another trial at the end of September, Malmo's public prosecutor said Friday, charged with "resisting arrest" at a July protest.

Police forcibly removed the 20-year-old campaigner from a climate rally in the Swedish port city on July 24.

"The protest was unauthorised and led to traffic being blocked. The young woman refused to obey police order to leave the site," said prosector Isabel Ekberg.

"This is therefore a case of refusal to comply."

Hours before the July rally, Thunberg received a court fine after a short trial and conviction for disobeying police at a previous protest at the same port on 19 June.

The rally, organised by environmental activist group Reclaim the Future, tried to block the entrance and exit to the busy port to protest against the use of fossil fuels.

The date for Thunberg's new trial has been set for September 27.

The activist shot to global fame after starting her "School Strike for the Climate" in front of Sweden's parliament in Stockholm at the age of 15.

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