UPDATE: 7.00 a.m. EDT - De Pere Fire Chief Alan Matzke said the fire that broke out in the century-old building woke up the people living in apartments in the building's second floor. The residents then alerted the other people living in the building. All the residents escaped and were also able to save their pets.

"As residents began to wake up, alert each other, law enforcement arrived on scene. Law enforcement assisted with those evacuations. They were able to assist most of the people out. By the time fire department arrived on scene we had a report that we potentially still had people trapped. We did not find anyone trapped. We were able to clear that building and ensure everyone's out. So at this point, all residents are accounted for. All residents are safe," he said in a news conference.

Matzke said the building’s ceiling had partially collapsed by the time the crews started fighting the blaze before it eventually collapsed. He added that the building posed a challenge for firefighters as it was 100 years old.

Calling it a “sad day,” De Pere Mayor Mike Walsh said, "This is a very historic, old building. Unfortunately when we have those kinds of buildings, it doesn't take long for them to go up when there's a fire. It's just a shame. I feel for the owner. I feel for the people who are leasing through that building and the ones who live in there."

Original story:

A 100-year-old building collapsed following a massive fire in De Pere, Wisconsin, in the early hours of Wednesday.

The fire broke out at the historic two-story building around 1.30 a.m. local time (2.30 a.m. EDT). The building contained a restaurant on the ground floor and apartments above it.

Officials said all the tenants in the apartments were evacuated before the entire building collapsed. Over 20 people residing in the area too were displaced, NBC 26 reported.

A firefighter reportedly sustained minor injuries while battling the blaze. The fire also resulted in the closure of all lanes in both directions on Highway 32 at Williams Street. Traffic to downtown De Pere was expected to be slow Wednesday.

Fire crews continued to battle the blaze. There was, however, no word on what caused the fire.