MIAMI BEACH (CBS4) – No word yet on what sparked a massive fire which destroyed a vacant building on Miami Beach.

Firefighters began battling the blaze in the 400 block of 21st Street just before 10 p.m. The fire reportedly started on the third floor of the building which used to be a hotel.  The building, which has been unoccupied for the last years, was recently undergoing some construction.

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At one point, fire crews were forced to evacuate the building when flames shot through the roof and firefighters feared it would collapse.

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Miami Fire Rescue spokesman Lt. Ignatius Carroll said Wednesday night that one of their main concerns was keeping the fire from spreading to nearby buildings.

“We’re trying to keep it contained in this area. We’re praying there is no one inside, as we understand it a lot of (homeless) stay here. The cause of the fire won’t be known for some time,” said Carroll.

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It took fire crews several hours to contain and finally put out the flames. While no nearby buildings were evacuated, people inside them were told to stay inside and keep their windows closed.