MINNEAPOLIS -- Firefighters spent hours early Monday morning battling a three-alarm fire in south Minneapolis, and now it is feared the iconic structure is in danger of collapse.

The fire started in the old Roberts Shoes building on the 700 block of East Lake Street at the intersection with Chicago Avenue around 10:30 p.m. Sunday.

Roberts Shoes, a Lake Street fixture, closed in 2014 after 77 years in business. Now it is home to a mix of apartments and businesses including a restaurant, dance studio, clothing store, hair salon and phone repair shop.

Crews arrived to find flames and heavy smoke billowing from the basement of the building. Firefighters originally mounted an interior attack but conditions were so hot and dangerous they were forced to retreat and battle the fire from the exterior.

Sunrise revealed the extent of the damage, which is significant. It appears the roof has fallen in, and a Captain told KARE 11's Ellery McCardle the entire building is in danger of collapse. Crews remain on the scene as of 11 a.m. to put down hot spots.

Everyone inside the building got out safely and no firefighters were hurt, but conditions were difficult with the stifling heat and humidity.

No word yet on the cause of the fire.