So far no injuries have been reported. An LFB spokeswoman said she also did not believe any animals were involved. The cause of the fire is not yet known.
A photograph posted on Twitter by LFB shows smoke billowing from the building as firefighters work at the scene.
The fire service said half of the roof of the cafe and shop was currently on fire.
London Zoo confirmed it was "currently dealing with an incident on site" and said it would "update as quickly as the situation allows".
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