The shots could be heard in video that was recorded by local reporters and protestors at the scene, after which two officers were seen on the ground.
The three officers were shot by someone with a rifle and wearing body armor, according to a Homeland Security bulletin obtained by BuzzFeed News.
The shootings occurred near a parking garage near El Centro College, according to the bulletin.
Local media reported the officers were rushed to the hospital.
Texas Lieutenant Gov. Dan Patrick confirmed on Twitter that officers had been shot, although details were not immediately available.
Police officers could be seen taking cover behind patrol cars as they responded to the incident.
Dallas police did not immediately respond to a request for comment by BuzzFeed News.
Maj. Max Geron, however, asked journalists not to broadcast officer positions as the department responded to the shooting.
Police had been actively tweeting about the protest in the downtown area, which was in response to two black men who were shot and killed by police this week in Minnesota and Louisiana.
This is a developing story. Check back for updates and follow BuzzFeed News on Twitter.