Protesters carrying signs reading “our forests are not for sale” broke through security lines of the COP30 UN climate talks on Tuesday night in Belém, Brazil.
BBC journalists saw UN security staff running behind a line of Brazilian soldiers, shouting at delegates to immediately leave the venue.
The UN told BBC News that the incident caused minor injuries to two security staff and limited damage to the venue.
Social media videos showed protesters who appeared to be from indigenous groups and others waving flags with the logo of a left-wing Brazilian youth movement called Juntos.
Protesters, some wearing what appeared to be traditional indigenous dress, stormed the COP30 entrance, chanting and kicking down doors, before tussling with security personnel, videos posted online showed.
Demonstrators crossed the first security barriers of the venue and were then prevented from getting further in, the UN told the BBC.
A security guard said he was hit in the head by a drum thrown by a protester, according to the Reuters news agency.
It is highly unusual security breach at a conference that has strict protocols.
Brazilian and UN authorities are investigating the incident, according to the UN.
Delegates from almost 200 countries are attending COP30 talks, which takes place 10 years after the Paris climate agreement, in which countries pledged to try to restrict the rise in global temperatures to 1.5C.
The talks are being held in Belém on the edge of the Amazon rainforest, which is home to dozens of indigenous groups, many of which any are vocal critics of the environmental damage caused by climate change and deforestation.
An indigenous leader from the Tupinamba community told Reuters, “we can’t eat money,” and that they were upset about development in the rainforest.
“We want our lands free from agribusiness, oil exploration, illegal miners and illegal loggers,” he said.
The meetings this year have been dubbed “the Indigenous peoples COP”, with Brazilian organisers promising to put indigenous people at the centre of the talks.
Brazilian President Luiz Inácio Lula da Silva told the opening of the summit that the world must “defeat” climate denialism and fight fake news.
He added that “COP30 will be the COP of truth” in an era of “misrepresentation” and “rejection of scientific evidence”.
At the opening ceremony, members of the Guajajara indigenous group, in traditional dress, performed a welcome song and dance for assembled diplomats.