PALMAS, Brazil (AP) — A noisy demonstration broke out Wednesday during the 100-meter dash competition at the World Indigenous Games, forcing a premature end to the day's events at what organizers have described as the indigenous Olympics.

The protesters, a boisterous crowd made up mostly of native Brazilians in traditional dress, were outraged over a land demarcation proposal that they say would be catastrophic for Brazil's 300 or so surviving tribes.

The proposed constitutional amendment would transfer the right to demarcate indigenous lands from the executive branch to Brazil's Congress, which is heavily influenced by the powerful big agriculture lobby that has fought against indigenous reserves in the past.

A committee in the Chamber of Deputies approved the proposal late Tuesday, though it must get through the full lower house and Senate, then be signed by President Dilma Rousseff in order to become law.

Brandishing handwritten banners against the proposal, around 100 demonstrators breezed past security guards and onto the floor of the sporting arena in Palmas. Hundreds of others ran to join the group as spectators cheered them on.

The announcer initially ignored the mass of protesters — although, dressed in feathers body paint, with some brandishing spears or bows and arrows, they proved impossible to ignore.

Narube Werreria, a young woman from the Karaja nation, scrambled up into the VIP area and seized the microphone to deliver a heated attack on the proposal.

"When we were here at the games, they were there in Congress plotting to steal our lands," she yelled. "Soon, there will be no more indigenous peoples, no more forest, no more animals."

The protest was loud but peaceful. After about 20 minutes, the demonstrators turned and filed quietly out of the arena.

The crowd of a couple thousand spectators booed when organizers finally announced an end to the day's activities, inviting the crowd to return Thursday.

Panamanian Cesar Cires had been slated to take part in a demonstration of the traditional games of his Ngabe-Bugle people, but his event was among the activities scrapped.

Still, Cires said he supported the demonstrators.

"We travelled a long way to be here, so it is a bit disappointing," he said. "But we as indigenous people understand our Brazilian brothers' plight. Next time, we'll join the protest, too."

Jenny Barchfield on Twitter: www.twitter.com/jennybarchfield