A manhunt is under way after two students were killed and nine other people wounded in a mass shooting at Brown University in Providence, Rhode Island, on Saturday.
The gunman opened fire in a classroom at about 4pm local time (21:00 GMT) in a building where exams were being held, police said.
Brown University, one of the oldest and most prestigious institutions in the United States, was placed under lockdown as officers searched the campus for the suspect, who remains at large.
Students in several parts of the campus were told to shelter in place, with police later escorting some people out of affected areas.
Officials at Rhode Island Hospital said most of those injured were in a “critical but stable” condition.
Authorities have not released the identities of those killed or injured.
“This is a day that we hoped never would come to our community. It is deeply devastating for all of us,” Brown University President Christina Paxson said in a statement.
Police have released limited information about the male suspect and have not confirmed his identity or a motive. It remains unclear whether he has any connection to the university.
CCTV footage showed the suspect leaving the building shortly after the attack, though his face could not be seen.
Providence Deputy Police Chief Tim O’Hara said the suspect was dressed entirely in black and may have been wearing a mask. He said the type of firearm used remains unknown and has not been recovered.
“We’re utilising every resource possible to find this suspect,” Mr O’Hara said, adding that additional armed officers had been deployed to search the area.
The shooting took place in the Barus and Holley building, part of Brown University’s engineering school, in a large first-floor classroom.
An economics professor told local public radio outlet Ocean State Radio that the shooting occurred during a review session for her course, led by her teaching assistant.
“He said that the shooter came in the doors, yelled something – he couldn’t remember what he yelled – and started shooting,” said Rachel Friedberg.
“Students started to scramble to try to get away from the shooter, trying to get lower down in the stadium seating, and people got shot,” she added.
Police cleared the building later on Saturday afternoon but did not find the suspect or the weapon.
Residents in the wider Brown University area were advised to remain indoors or stay away until the shelter-in-place order is lifted.
In a statement, the university said police would enter non-residential buildings to escort people to safe locations.
Steph Machado, a reporter for the Boston Globe, told BBC News that restaurants near the campus had locked their doors, with staff and customers waiting inside.
“There are flashing lights everywhere,” she said.
In the immediate aftermath of the shooting, reports suggested a suspect had been taken into custody, but police later confirmed the individual detained was not involved.
Mari Camara, a 20-year-old Brown University student from New York City, told the Associated Press she was leaving the library when she rushed into a nearby restaurant to seek shelter, where she hid for about three hours.
“Everyone is the same as me, shocked and terrified that something like this happened,” she said.
University exams scheduled for Saturday were cancelled, provost Frank Doyle said.
President Donald Trump, speaking to reporters as he returned to the White House after attending the annual Army-Navy football game, described the shooting as “a terrible thing”.
“All we can do right now is pray for the victims and for those that were very badly hurt,” he said.
Rhode Island Governor Dan McKee said in a statement: “Our capital city experienced an unthinkable tragedy today. Our hearts are with the people of Providence and all those impacted.”
Brown University, a member of the Ivy League, has more than 11,000 students and is located in Providence, Rhode Island’s capital, about 50 miles (80km) from Boston and 180 miles (290km) from New York City.
The attack brings the number of mass shootings in the United States this year to 389, according to the Gun Violence Archive.
The group defines a mass shooting as an incident in which four or more people are killed or injured, excluding the attacker.
