The fire at Chessington World of Adventures on Saturday was caused by a heater, London Fire Brigade (LFB) believes.
The fire, which broke out at the Creaky Café at about 8.30am, gutted the building and forced the evacuation of zoo animals.
Two reindeer were also rushed to safety.
Fire investigators believe the fire was caused by items being left too close to a heater.
An LFB spokesman said: "You should always make sure heaters are kept well away from furniture or fabric, as they can heat up and catch fire."
The plume of smoke from the fire was visible from Surbiton fire station, firefighters said.
Park visitors were turned away at the gates by security staff.
The park will be closed to day visitors for Christmas following the fire.
Photo: London Fire Brigade
The park’s Festive Zoo Days will reopen on Boxing Day. Customers who have already booked package deals will still be able to visit the zoo, and Christmas entertainment in the park’s hotel will continue as planned.
People who had booked tickets for a day visit will be able to get a full refund.
London Fire Briagde's advice on heaters
- Heaters should stand where they can't be knocked over, away from beds, furniture and fabrics.
- Do not put anything on the heater or use it to dry clothes.
- Never sit too close to the heater as you could set light to your clothes or chair, especially if you fall asleep.
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