Two firefighters were shot and killed and two others hospitalized after a gunman targeted them as they responded to a fire he is believed to have set to a home and a car in Webster, N.Y., police said.
"It does appear that it was a trap that was set for first responders," Police Chief Gerald L. Pickering said.
SWAT team officers used an armored personnel carrier to evacuate 33 residents from homes in the area.
"Upon arrival all [the firefighters] drew fire, all four were shot on the scene," Pickering said. "One was able to flee the scene. The other three were pinned down."
An off-duty police officer responding to the call was also injured by shrapnel and was being treated.
Pickering said the gunman was dead at the scene, but had yet to be identified. The shooter died of a gunshot wound, but police didn't yet know if "it was self inflicted or not."
The firefighters, all volunteers, continued to fight the blaze that engulfed three other homes and damaged three more on a sleepy street next to Lake Ontario that police described as a quiet vacation community.
Police had not yet determined the "weapon or weapons" the gunman used and had not fully investigated the scene because the fires continued to rage.
"I know many people are going to be asking if they were assault rifles," Pickering said, following a week-long debate about such weapons after one was used in a tragic school shooting in Newtown, Conn. on Dec. 14.
Among the dead firefighters was Lt. Michael Chiapperini, a 20-year veteran of the Webster Police Department and "lifetime firefighter," according to Pickering. Chiapperini was a spokesman for the police department, ABC News affiliate WHAM reported.
Police identified the other firefighter killed as Tomasz Kaczowka, who WHAM reported also was a 911 dispatcher.
The chief, choking up, called the incident that shattered the quiet before 6 a.m. on Christmas Eve morning "terrible."
"People get up in the middle of the night to fight fires," he said. "They don't expect to get shot and killed."
Two surviving firefighters were in the intensive care unit at Strong Memorial Hospital in Rochester, N.Y. Both men were awake and breathing on their own after surgery and were in what doctors are calling "guarded condition."
Joseph Hofsetter was shot once and sustained an injury to his pelvis and has "a long road to recovery," said Dr. Nicole A. Stassen, a trauma physician.
The second firefighter, Theodore Scardino, was shot twice and received injuries to his left shoulder and left lung, as well as a knee.
New York Gov. Andrew Cuomo released a statement calling the attack a "senseless act of violence" and the first responders "true heroes."