Police in Rhode Island were searching for a suspect late on Saturday after a shooting at Brown University in Providence left two students dead and eight others critically wounded at the Ivy League school, officials said. A ninth person was hurt by bullet fragments, the mayor said.

Streets around campus remained blocked and packed with emergency vehicles hours after the shooting and law enforcement officials heightened security around the city as police continued their manhunt.

“The individual responsible is still at large,” Mayor Brett Smiley told reporters at a 9:30pm (7:30am PKT) press conference. Deputy Police Chief Timothy O’Hara said the suspect had not been identified.

Officials said they are looking for a male dressed in black and were releasing a video of the suspect, who O’Hara said may have been wearing a mask. He said officials had retrieved shell casings from the scene of the shooting, but that police were not prepared to release details.

Officials said the gunman escaped after shooting students in Brown’s Barus & Holley engineering building, where exams were taking place at the time.

“We are a week and a half away from Christmas. And two people died today and another eight are in the hospital,” Smiley said earlier in the evening. “So please pray for those families.”

Brown is on College Hill in Providence, Rhode Island’s state capital. The university has hundreds of buildings, including lecture halls, laboratories and dormitories.

“This is the day one hopes never happens, and it has,” Brown’s president Christina Paxson told reporters, confirming all or nearly all of the victims were students.

As news of the shooting spread, the school told students to shelter in place.

Brown student Chiang-Heng Chien told local TV station WJAR he was working in a lab with three other students when he saw the text about the active shooter situation a block away. They waited under desks for about two hours, he said.

Rhode Island Governor Daniel McKee vowed that the shooter would be brought to justice. “We’re going to make sure that we catch the individual that brought so much suffering to so many people.”

The search for the suspect was hampered in part because downtown Providence was crowded with holiday shoppers and thousands of people attending concerts, local media said. Federal law enforcement and police from surrounding cities and towns were assisting in the search, officials said. According to local news reports, venues across the city were bringing in extra security.

President Donald Trump told reporters at the White House that he had been briefed on the situation, which he called “terrible”.

“All we can do right now is pray for the victims and for those that were very badly hurt.”

Compared to many countries, mass shootings in schools, workplaces, and places of worship are more common in the US, which has some of the most permissive gun laws in the developed world. The Gun Violence Archive, which defines mass shootings as any incident in which four or more victims have been shot, has counted 389 of them this year in the US, including at least six such shootings at schools.

Last year the US had more than 500 mass shootings, according to the archive.