Columbia University officials threatened to expel activists on Tuesday after they seized and occupied an academic building as the standoff between administrators and student protesters intensified.

Shortly after midnight on Tuesday, protesters broke windows and entered Hamilton Hall, where they unfurled a banner reading "Hind's Hall", symbolically renaming the building for a six-year-old Palestinian child killed in Gaza by the Israeli military.

Outside the academic building - the site of various student occupations dating back to the 1960s - protesters blocked the entrance with tables, linked arms to form a barricade and chanted pro-Palestinian slogans.

A university spokesperson said protesters had chosen to escalate an "untenable situation" and that the school's top priority is the safety and order on campus.

"The work of the university cannot be endlessly interrupted by protesters who violate the rules. Continuing to do so will be met with clear consequences," school spokesperson Ben Chang said in a statement.

Chang said students occupying the building face expulsion.

One of the lead negotiators for the coalition of student protest groups said Columbia officials contacted him through mediators to ascertain the demands of the activists occupying Hamilton Hall.

"Once they decide to come back to the table we can talk about demands," said Mahmoud Khalil, who said he was off-campus. "These students felt hurt and abandoned by the administration because it did not listen to their demands, so they had to do things differently."

On Monday, Columbia University began suspending pro-Palestinian student activists, including Khalil, for refusing to dismantle the protest camp on the campus after the Ivy League school declared a stalemate in talks seeking to end the demonstration.

University President Nemat Minouche Shafik said in a statement that days of negotiations between student organizers and academic leaders had failed to persuade demonstrators to remove the dozens of tents set up to express opposition to Israel's war in Gaza.

Protesters on the Manhattan campus are demanding that Columbia meets three demands: divestment from companies that support Israel's government, transparency in university finances, and amnesty for students and faculty disciplined for their part in the protests.

Shafik this week said Columbia would not divest from finances in Israel. Instead, she offered to invest in health and education in Gaza and make Columbia's direct investment holdings more transparent.

After students entered the Columbia building, the school sent out a notice saying access to the campus had been limited to students residing in residential buildings on campus and employees providing essential services.

New York City police officers arrived outside the school gates in unmarked cars moments after the protesters entered the building, the Columbia Spectator newspaper reported. Police told the paper they would only enter school grounds if someone was injured.

MORE PROTESTS, MORE ARRESTS

The building occupation at Columbia is at the center of Gaza-related protests roiling university campuses across the US in recent weeks.

Students at dozens of campuses from California to New England have set up similar tent encampments to demonstrate their anger over the Israeli operation in Gaza.

The pro-Palestinian rallies have sparked intense campus debate over where school officials should draw the line between freedom of expression and hate speech.

At Cal Poly Humboldt University, police early on Tuesday swarmed the campus, where students were occupying a school building, and starting detaining people, local media reported.

Police late on Monday had declared the protest an unlawful assembly and warned people they faced arrest if they did not disperse.

The campus was earlier closed to all people except students and faculty because of the ongoing protest. Information was not immediately available on how many people may have been detained.

Civil rights groups have criticized law enforcement tactics on some campuses where police have clashed with protesters and have used chemical irritants to disperse crowds.

Arrests continued at a number of schools across the country.

Police detained about 30 protesters at their encampment at the University of North Carolina in Chapel Hill early on Tuesday after the university gave them until 6 a.m. local time to disperse, according to a statement from the school, noting that students had trespassed into classroom buildings overnight.

At the University of Texas at Austin, police arrested dozens of students whom they doused with pepper spray at a pro-Palestinian rally on Monday.

Protesters also squared off with police at Virginia Commonwealth University in Richmond. Police used chemical irritants on the crowd and detained numerous people. The protesters had set up a "liberation zone" of tents surrounded by barriers.

“After repeated warnings and refusal to disperse, law enforcement must protect Virginians," Virginia Governor Glenn Youngkin, a Republican, wrote on social media after the incident.