Ten law enforcement officers in Dallas were shot, three fatally, by what is believed to be two snipers near the end of a demonstration over police killings of black men was ending, Dallas police said.

by Phil Helsel

(NBC News) - The shooting occurred at around 9 p.m. (10 p.m. ET) as a rally and march downtown was ending, NBC Dallas-Fort Worth reported.

Four DART police officers were shot in downtown Dallas. 1 deceased, others not life-threatening. No IDs yet. Updates via twitter.

— dartmedia (@dartmedia) July 8, 2016

A large number of law-enforcement vehicles and personnel could be seen at the scene. The demonstration and march was ending at the time.

A person at the protest said they were “making our second lap” when gunfire erupted.

“We heard shots, we smelled gunpowder, and that’s when everything got really intense and surreal,” the witness told MSNBC. “We just started to run and grab kids,” he said.

#BREAKING 2 police officers have been shot in downtown Dallas: Officer at scene https://t.co/r4xNZlGM72 pic.twitter.com/DOUQhczKJx

— NBC DFW (@NBCDFW) July 8, 2016

Dallas Area Rapid Transit suspended bus and rail service downtown “due to criminal activity,” DART said in a Twitter message.

Several hundred people had gathered at park and march Thursday in reaction to the police shootings of Alton Sterling in Baton Rouge Tuesday and Philando Castile in a St. Paul suburb.

The demonstration in Dallas was one of several held in cities across the county Thursday.

Dallas Police cruiser outside Parkland Hospital ER. Others around side of hospital. @NBCDFW pic.twitter.com/MNmdxOqupo

— ScottGordonNBC5 (@ScottGordonNBC5) July 8, 2016

In Saint Paul, Minnesota, a crowd estimated to be more than a thousand strong gathered outside a school where one of those men killed, Philando Castile, worked as a kitchen supervisor.

Castile was fatally shot by a police officer in a suburban city during a traffic stop, and video showing him wounded and slumped over in his car evoked nationwide outrage.

“The kids called him Mr. Phil, everyone called him Mr. Phil, and he was a fantastic man; he was a friend to every single child that came through that line,” one woman who knew Castile told NBC affiliate KARE outside the J.J. Hill Montessori School. “If there was a kid that was hungry that didn’t have money for food he was helping out.”