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It's across the top center section of the hotel. Putting out a good bit of smoke, but it appears to be contained primarily to the façade.
 
Now there saying that Traffic from Tropicana to Harmon is beging deverted

The top 4 stories are starting to catch on fire
 
It definitely looks like it's spreading now. Of course, if the firefighters haven't been able to do anything yet to supress the flames then that would make sense. Hopefully they'll be able to contain it soon...
 
It's pretty clear that it's just the façade...looks to be extremely flammable. Should be mostly superficial damage though if they can get it under control.

The lower sections are burning because flaming debris is landing on a ledge four floors down and catching there.
 
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