Pro-Palestinian protesters occupy building at Columbia University

Pro-Palestinian activists occupied a building at Columbia University early on Tuesday, escalating a battle with administrators who have begun suspending students for refusing to dismantle tents set up on the New York campus.

Protesters entered Hamilton Hall - the site of student protests dating back to the 1960s - and suspended a banner reading "Hind's Hall" from an upper floor. Others outside blocked the doors with outdoor tables and linked arms to form a barricade in front.

"This building is liberated in honour of Hind, a six-year-old Palestinian child murdered in Gaza by the Israeli occupation forces funded by Columbia University," a protester shouted from inside, with those outside repeating each phrase.

Israel has denied targeting civilians in its war on Hamas militants in Gaza, accusing the militants of hiding among them.

Minutes after the protesters gained access to the building, New York City police officers arrived outside the school gates in unmarked cars, the Columbia Spectator newspaper reported. It said police told the paper they would only enter school grounds if someone was injured.

Some three hours after the students entered the building, the school sent out a notice saying that effective immediately access to the Morningside campus has been limited to students residing in residential buildings on campus and employees providing essential services.

"This access restriction will remain in place until circumstances allow otherwise," it said. "The safety of every single member of this community is paramount. We thank you for your patience, cooperation and understanding."

On Monday, the university began suspending pro-Palestinian student activists who refused to dismantle a 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.

The crackdown at Columbia, at the center of Gaza-related protests roiling university campuses across the U.S. in recent weeks, came as police at the University of Texas at Austin arrested dozens of students whom they doused with pepper spray at a pro-Palestinian rally.

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.

The arrests came after police late on Monday declared that the protest was unlawful assembly and warned people that if they did not disperse they wold face arrest.

The campus was earlier closed to all people except students and faculty because of the ongoing protest. Neither the school nor a police spokesman was immediately available for comment or to detail how many people may have been detained.