He wrote: 'Such a shame, huge fire at Chester Zoo.
The Zoo themselves have said this afternoon: "The zoo's teams are now assessing the situation".
Frank Riding was visiting the zoo and said the fire was growing at "speed".
In a statement, the zoo said: "Sumatran orangutans and other mammals are all accounted for".
Chester zoo boast they are the the largest indoor zoo exhibit in United Kingdom history, with thousands of tropical animals and plants on display.
'Visitors have been evacuated and asked to leave the zoo as teams work to bring the situation under control. We working hard to account for all other species.
Firefighters at Chester Zoo after a fire broke out in the Monsoon Forest habitat area of the zoo, in Chester, England, Saturday Dec. 15, 2018.More news: Time to Change Your Password: 25 Worst Passwords of 2018 Revealed
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David Wearing filmed the building going up in flames, and said: 'Hope humans and animals evacuated safely - fire crews arriving on their scene'.
Cheshire Fire and Rescue have now confirmed that there are no injuries as a result of the incident.
It added that visitors were asked to leave the zoo and staff were now in the process of moving animals away from the incident.
The zoo tweeted the blaze was in its Monsoon Forest habitat. The fire has now been extinguished, but fire fighters will remain on site throughout the night alongside the zoo's experts.
"The zoo's The Lanterns event this evening has been cancelled and ticket holders notified by email".
"The fire was reported at 11.28am and there are now 15 fire appliances in attendance at the scene".
"I would also like to thank staff at the zoo for their swift response and for all of their help and assistance in bringing this situation under control".