Chimpanzees, orangutans, a gorilla, bats and birds were among the animals who died at Krefeld Zoo, near the Dutch border. Two chimpanzees, Bally and Limbo, survived, the zoo said.
Describing the fire as an "incomprehensible tragedy", it
said the cause was not known.
Local broadcaster WDR said investigators were exploring the possibility it had been started by a celebratory firework.
The blaze destroyed the monkey enclosure, which opened in 1975, shortly before midnight.
But firefighters prevented the flames from spreading to other buildings at the zoo in North Rhine-Westphalia.
The zoo would remain closed during Wednesday with employees "in shock" after a "terrible tragedy", the management said.
With additional input from AFP
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