Update 2:33 p.m.:

From ABC 7's Stephen Tschida:

A Fire truck responding to a call collided with a packed Metrobus along 14th Street in D.C.'s Brightwood neighborhood Wednesday morning, sending 22 people to the hospital.

Passengers say the bus driver apparently didn't hear the fire engine's siren as it ran a stop sign while traveling east on Madison.

"The driver, he faint, so I thought he was dead. But I think he is alive," said Metrobus passenger Irene Jaqez.

None of the injuries, including the bus driver's, was life-threatening, according to Fire and EMS officials. Most suffered neck and back problems, or cuts and bruises.

But passengers describe a chaotic and frightening scene after the collision:

"I fell on the floor, so I just woke up and I see the people, the guys helping us to get off (the bus)," Jaqez recalled. "There was a women on top of me; she had a hurt neck."

While the bus had the right of way, the fire truck had its siren activated as it responded to a pedestrian struck call, according to witnesses. The fire engine was at a training session a couple of blocks away, and was not traveling very fast at the time of the crash. Witnesses differ on how long the siren was activated before the crash.

The collision remains under investigation by D.C. police and Metro Transit Police.

Via @dcfireems: 14th St & Madison St Metro Bus - multiple inj (12) - Mass Casualty incident - addl units responding

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DC Fire/EMS is currently evaluating 12 injured riders from the Metrobus that crashed.

10:43: DC Fire/EMS reports that none of the injuries are serious and several of the riders are being checked out as a precaution.

11:04: ABC reports that the accident at 14th and Madison St. NW occurred when a fire truck was heading to the scene of a pedestrian accident at 13th and Madison NW. The bus driver was among the injured.

The struck pedestrian was an adult female who does not have life-threatening injuries.

12:30: DC Fire/EMS tweeted that 25 people were evaluated at the scene of the bus crash. 18 passengers, the bus driver, and 4 firefighters were transported for evaluation.