More than 400 law enforcement personnel were deployed on Saturday as police sought the suspect in a shooting at Brown University in Rhode Island that left two students dead and another nine people wounded at the Ivy League school, officials said.

The Providence university remained in lockdown hours after a suspect with a firearm entered a building where students were taking exams.

Officials do not believe there is any "specific, ongoing threat" from the suspect, Providence Mayor Brett Smiley said late Saturday, but with law enforcement agencies canvassing the area and conducting a manhunt, a shelter-in-place order for the campus and the surrounding neighborhood will remain for now.

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"The shelter-in-place allows (law enforcement) to do their work in the first phase of the investigation," Smiley said.

Streets around the campus were packed with emergency vehicles and security was heightened around the city as law enforcement agencies sought the gunman, who has not yet been identified, officials said.

Agents from the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco, Firearms and Explosives are working with local and state police on the investigation.

Officials released a video of the suspect, a male possibly in his 30s and dressed in black. Providence Deputy Police Chief Timothy O’Hara said the individual may have worn a mask, but officials are not certain.

Investigators retrieved shell casings from the scene of the shooting, but police are not prepared to release details yet, O'Hara said.

The gunman escaped after shooting students in a classroom in Brown's Barus & Holley engineering building, where outer doors had been unlocked while exams were taking place, officials said.

Detectives are looking into why that location was targeted, police Chief Oscar Perez told reporters at a news conference.

All or nearly all of the victims were students, Brown President Christina Paxson told reporters.

"This is the day one hopes never happens, and it has," Paxson said.

Seven of the nine wounded were listed as critical late Saturday, according to Brown University Health.

Brown, located on College Hill in Rhode Island's state capital, has hundreds of buildings, including lecture halls, laboratories and dormitories.

The shooting suspect is thought to have fled, according to local officials, along a normally bustling street of restaurants and coffee shops.

UNDER DESKS FOR HOURS

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 complicated by throngs of holiday shoppers and thousands of people attending concerts and events on a weekend night, local officials told reporters.

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.

Police were scouring videos and calling for information from witnesses or others in their search for the suspect.

"Some tips have been coming in. We have been running them down," O’Hara said. "None of them have worked out for us yet."

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.

"I’m numb, and I’m more so angry," Brown sophomore Zoe Weissman told Reuters.

Weissman has testified before state lawmakers in support of an assault weapons ban about her experience as a middle schooler in Parkland, Florida, where a shooter in 2018 killed 17 students and teachers, and injured others.

"I’m shocked but I’m not surprised."