Over 15,000 demonstrators marched in Copenhagen toward the US Embassy, according to Greenland's public broadcaster KNR.
Protests also unfolded in Danish cities including Aarhus, Odense, and Aalborg, as well as in Greenlandic communities such as Nuuk, Aasiaat, Qaqortoq, and Ilulissat, Danish broadcaster TV2 reported.
Crowds waved Greenlandic flags and carried signs with messages like "Hands off Greenland" while repeatedly chanting that Greenland belongs to its people.
In Nuuk, Greenland's capital, large gatherings were expected later in the day as residents aimed to send a clear message to Washington.
The demonstrations highlighted widespread opposition to any US takeover of Greenland, a self-governing territory under the Kingdom of Denmark.
Greenland has drawn US attention because of its strategic Arctic location, rich mineral resources, and concerns over potential Russian or Chinese influence in the region.
Trump has repeatedly stated that the United States needs to acquire Greenland for national security reasons and to block rivals from gaining a foothold.
Denmark and Greenland have firmly rejected any sale, insisting on Danish sovereignty.
A bipartisan US congressional delegation arrived in Copenhagen on Friday amid the ongoing tensions.
The lawmakers met with Danish business leaders at the Confederation of Danish Industry after traveling from parliament.
US Democratic Senator Dick Durbin of Illinois emphasized longstanding alliances.
“We have been friends and allies with Denmark and Greenland for decades. We want them to know that we greatly appreciate that,” Durbin said.
He added that recent remarks by President Donald Trump “do not align with what the American people feel and believe.”
Danish parliament speaker and former defense minister Soren Gade expressed a shift in his perspective.
“I never thought I would speak critically about the United States. But if I am to be able to look Danish veterans in the eye in the future, I can no longer remain silent,” he wrote on Facebook.
Gade called the US tone “indecent.”
After the meeting, Republican Senator Thom Tillis of North Carolina described Trump’s threats as “absurd," saying "because Greenland is a sovereign territory and a nation."
When asked if Denmark and Greenland should take the threats seriously, Tillis said many in Congress would prevent any such action.
Christian Friis Bach, chairman of the Danish Foreign Policy Committee, noted the goal was to send a strong message back to the US
“We hope they return with strong images and strong messages that can convince even more members of Congress that Greenland cannot be taken over,” he added.
US special envoy to Greenland Jeff Landry told Fox News he plans to visit the island in March.
“I believe that a deal can and will be made,” he said.
Landry also said that “the president is serious” about wanting Greenland.
The White House has stated that recent European troop deployments to Greenland would not change Trump's plans.
Germany, France, Sweden, and Norway announced this week they would send a joint mission to the island following unsuccessful talks between US, Danish, and Greenlandic officials.