NORTHAMPTON — Hundreds of students occupied Smith College’s administration building on Wednesday, demanding that the college divest from military contractors and weapons manufacturers they say are aiding in the slaughter of Palestinians in Gaza.

The students plan to occupy College Hall until their demands are met or until they are arrested and removed. The building was scheduled to close at 5 p.m.

Around 3:45, Ruby Masters, an organizer with Students for Justice in Palestine, said college officials had already locked all the doors after most of the occupiers left to get supplies for the overnight stay in the building.

A large crowd then gathered for a rally outside College Hall. After 5, Masters said there were 45 to 50 people planning to stay in the building overnight. Authorities were not allowing anyone or anything into the hall and planned to keep the building closed Thursday, she said.

Masters said the action followed the college trustees’ denial of the justice group’s request that they pull Smith’s investments from weapons contractors such as General Dynamics, Lockheed Martin and Boeing.

Masters said it took a significant amount of time and effort for the group to draw up its proposal. In an emailed response Tuesday, she said, the board of trustees said its Advisory Committee on Investor Responsibility had determined that “the request did not meet the threshold for taking action and also found that the endowment’s investment in military contractors and weapons manufacturers is negligible and entirely indirect.”

Wednesday’s action began with a walkout at 11:45 a.m., with students gathering at the Campus Center to listen to speakers on the impact of the Smith community on Palestinians in Gaza.

Afterward, a column of 300 to 400 students marched to College Hall, chanting, “From the river to the sea, Palestine must be free!” “Hey, hey, ho, ho, occupation has got to go!” and “Shut it down!”

Inside the hall, Masters said most of the internal doors leading to offices were closed, and many employees had left the building.

She said the walkout and sit-in had drawn almost double the number of people who joined the group’s first rally.

In a statement, college authorities said they support and endorse freedom of thought and expression but warned against disruption.

“Any person at Smith College is free to express opinions and support causes by orderly means that do not disrupt the regular and essential operation of the institution,” the statement read.

Masters, a sophomore from Seattle, linked the sit-in to a tradition of protest at Smith, including an anti-apartheid sit-in at College Hall in 1986 that eventually forced the college to divest from companies that did business with South Africa.

“Unfortunately, justice is disruptive,” she said.