Firefighters are in attendance at the animal attraction near Ladybank, after a fire was reported at around 12.10pm on Sunday afternoon.
Four fire crews are tackling the blaze in the building which houses the soft play facilities.
All visitors have been evacuated from the zoo, and keepers safely evacuated the marmosets, which were in the enclosure closest to the fire, as the blaze broke out.
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In a post on social media Fife Zoo said: “All humans and animals are safe. All emergency teams are on site to contain the fire. Thank you for the concern.”
One eyewitness said: "There is smoke and flames pouring out of the soft play building.
“Luckily the keepers were able to evacuate the marmosets safely. Their enclosure was closest to the site of the fire.
“It looked at one point like the firefighters had got the blaze under control, but the flames have now taken hold of the building.
"It's a devastating blow for the owners, with the facility only in its infancy."
The zoo reopened to visitors on June 29 following months of being closed due to the Covid-19 pandemic.
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