Police in the US state of Rhode Island were searching for a suspect in a shooting at Brown University in Providence in which two people died and eight were critically wounded at the Ivy League school.

Providence Mayor Brett Smiley told a news conference that police were still searching for the shooter, who struck at Brown's Barus & Holley engineering building, where exams were taking place at the time.

Officials said police were looking for a male dressed in black and were scouring local video cameras in the area for footage to get a better description of the suspect.

Smiley said officials could not yet disclose details about the victims, including whether they were students. He lamented the shooting.

"We are a week and a half away from Christmas. And two people died today and another eight are in the hospital," he said. "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.

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

Brown University student Chiang-Heng Chien told local media 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.

US 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 America, including at least six such shootings at schools.

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

Complicating the manhunt, local media reports said downtown Providence was crowded with holiday shoppers and thousands of people attending concerts.

US federal law enforcement and police from surrounding cities and towns were assisting in the search, officials said. (Reuters)