Nearly 20 displaced, firefighters injured during 3-alarm blaze in Allentown, Pennsylvania

ALLENTOWN, Pennsylvania (WPVI) -- Fire officials said about 20 people are out of their homes after an intense fire that injured several firefighters Monday evening in downtown Allentown.

The fire broke out at around 5:30 p.m. along the 1100 block of Hamilton Street.

A mix of residential and office buildings were damaged, officials said.

Some residents reported hearing an explosion right before they saw flames.

Black smoke could be seen for miles as the fire quickly spread, taking several hours to get under control.

Firefighters arrived to heavy smoke and flames shooting from the roof.

A box truck out back also caught fire.

Fire officials said four to five buildings were damaged due to fire, smoke or water that was sprayed during firefighting efforts.

"We're trying to make sure everything's OK down there because they did have kids. That's our main concern is the kids," said neighbor Arlene Reed.

We're told one civilian was taken to the hospital with non-life-threatening injuries, but officials have not released an age.

Officials said five firefighters were also taken to the hospital due to high heat and are expected to be OK.

Outside temperatures reached over 90 degrees, which made conditions more dangerous for crews and impacted air quality in the city.

One dog was also rescued, officials said.

Employees at law offices next door are working remotely on Tuesday because their building was also damaged.

Fire officials are still investigating the cause.