An ambulance from Prince George's County had to transport an injured D.C. police officer to the hospital Tuesday night after District authorities said they had no units available to respond.

The incident began at about 6:30 p.m. when a car struck the male officer at 46th and A streets in Southeast Washington.

Emergency dispatchers determined within minutes there were no ambulances available to respond and asked authorities in Prince George's County for assistance, according to people familiar with the episode, who spoke on condition of anonymity because they were not authorized to speak publicly.

The ambulance, the sources said, arrived on the scene 18 minutes after the initial call about the injured officer came in to dispatchers.

Mark Brady, a spokesman for the Prince George's County Fire and Emergency Medical Services Department, confirmed his agency aided D.C. authorities after receiving a request for help.

"We did go into the District," Brady said. "D.C. asked for assistance with a basic life support unit."

Brady said the Prince George's ambulance, joined by a D.C. paramedic, took the injured officer to a trauma center in Washington for treatment. A police spokesman said the officer was "conscious and breathing," but he did not have further details.

Spokesmen for Mayor Vincent Gray and the D.C. Fire and Emergency Medical Services Department did not immediately respond to requests for comment Tuesday night.

But Kristopher Baumann, the leader of the District's police union, slammed the city's response and blamed Fire Chief Kenneth Ellerbe for the episode.

"At this point, Chief Ellerbe has pushed the fire department into a place where it cannot perform even the most basic services. From everything we've seen, it has been one misstep, one act of mismanagement after another," Baumann said. "We are now in a situation where a police officer is laying out in the cold, out in the street, because the fire chief can't provide ambulances."

Edward Smith, the president of the firefighters union, said he hoped the incident would spur the city to increase the number of available ambulances.

"We hope there are more units available in the future for timely transport," he said. "It's a matter of public safety."