The protests were the latest salvo in a yearslong fight that pits scientific discovery against cultural preservation.
Scientists hope the massive telescope planned for the site, a world-renowned location for astronomy, will help them peer back to the time just after the Big Bang and answer fundamental questions about the universe. But some Native Hawaiians consider the land holy, as a realm of gods and a place of worship.
The protesters gathered in response to an announcement by the state that officials would close the road to the summit of Mauna Kea on Monday so they could begin bringing equipment to the construction site in coming days.
At about daybreak, a group of kupuna, or elders, sitting in chairs, tied themselves together with rope and blocked the road to the summit in hopes of preventing construction equipment from getting past. Another group of protesters spent the day lying prone on the ground, with their arms shackled under a grate in the road.
After two protest leaders spoke with police, they addressed the crowd and told them anyone who didn't move would be arrested. The group would move aside, but the elders were expected to remain, protest leaders Kaho'okahi Kanuha and Andre Perez said.
By mid-afternoon, law enforcement hadn't arrested anybody, saying their priority was installing concrete barriers along a nearby highway to create a buffer between speeding cars and the large numbers of people congregating in the area.
Those on the grate left after being told they wouldn't be arrested.
Walter Ritte, an activist, said it was difficult lying there for 11 hours. He said protesters' arms were connected through a series of metal pipes under the grate. Authorities would have had to cut the pipes to remove them, he said.
"It was so cold at 4 o'clock in the morning," Ritte said. "It was a test of our fortitude. This mountain is like our last stand."
Telescope opponent Jennifer Leina'ala Sleightholm said she hoped peaceful protests would lead to an end of the project while acknowledging that was an unlikely scenario.
"I think I know what will happen, but what I hope will happen is I hope that they would just turn around and save our kupuna," she said, using the Hawaiian word for elders.
Protesters vowed to return on Tuesday.
Richard Ha, a Native Hawaiian farmer who supports the project, said he's encouraged that there seems to be some cooperation between protesters and law enforcement.
He said he sympathized with the protesters, but is hopeful construction will begin.
It can be hard for Native Hawaiians to support the telescope because they fear backlash for being perceived as opposing Hawaiian beliefs, he said.
"It's very difficult when you have family members on different sides," he said.
The project has been delayed by years of legal battles and demonstrations, drawing attention from the likes of "Aquaman" actor Jason Momoa, who has Native Hawaiian ancestry and has voiced opposition to the telescope.
Scientists selected Mauna Kea in 2009 after a five-year, worldwide search for the ideal site.
Protests disrupted a groundbreaking and Hawaiian blessing ceremony at the site in 2014. After that, the demonstrations intensified.
Construction stopped in April 2015 after protesters were arrested for blocking the work. A second attempt to restart construction a few months later ended with more arrests and crews pulling back.
Hawaii's Supreme Court has ruled the construction is legal, permits are in place, and the state has given the company behind the telescope a green light to resume building. The company is made up of a group of universities in California and Canada, with partners from China, India and Japan.
Ancient Hawaiians considered the location kapu, or forbidden, according to the University of Hawaii. Only the highest-ranking chiefs and priests were allowed to make the long trek to Mauna Kea's summit above the clouds.
Today, the university leases the land at the summit from the state for existing telescopes and observatories on the summit. A road built for telescope access decades ago is used by thousands of tourists and locals each year, including Native Hawaiians who go there to pray.
Supporters of the $1.4 billion telescope say the cutting-edge instrument will not only make important scientific discoveries but bring educational and economic opportunities to Hawaii.
The telescope's primary mirror would measure 98 feet (30 meters) in diameter. It would be three times as wide as the world's largest existing visible-light telescope, with nine times more area.
Gov. David Ige has said unarmed National Guard units would be used to transport personnel and supplies and enforce road closures but would not be used in law enforcement capacity during what could be weeks of protests.
In a news conference Sunday, Ige said that he "respected the right of people to protest" at the telescope site as long as protesters behave lawfully.
"As construction begins, our number one priority is keeping everyone safe," Ige said, adding that he wants to make sure construction workers and truck drivers have unimpeded access to the telescope site.
Kelleher reported from Honolulu.
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