The talk show host went live Wednesday morning in an unconventional fashion -- more somber than usual with no graphic backing her onstage ... and the reason for that is because there was an emergency on set at ABC Studios in NYC.

Check out the clip ... Hall explains a grease fire in the kitchen forced her staff and the show's audience to evacuate entirely, and brought multiple firetrucks to the scene.

TH says the show's staff was totally in place while her audience stood outside the doors, ready to enter, when the fire derailed their plans ... though she assures her viewers everyone's doin' just fine.

Tamron explains the team's in the middle of cleaning up the mess, and the network would air Monday's episode instead of the new "Tamron Hall" they'd planned to shoot.

She also posted a couple vids to her Instagram Story after she evacuated the building ... saying she feels like she's back in her hard news reporting days, and filming as first responders arrived on the scene, while a bunch of people were milling around outside.

BTW ... the blaze caused more than just 'Tamron Hall' to evacuate -- "The View" hosts walked out to Billy Joel's "We Didn't Start the Fire" this morning 'cause they had to bail out too. Goes without saying ... they shoot their program at the same address.