Twycross Zoo was closed to the public after "some chimpanzees" got into an area where they should not have been.
A spokeswoman for Leicestershire Police said: "A call came in at 9.35am from the zoo to let us know that some chimpanzees, that were in the process of being moved from one building to another.
"In the process of this they have perhaps gone into an area of that building that they shouldn't have been in.
"They don't appear to have actually physically escaped. As a precaution, we've been called by the zoo."
The spokeswoman said they stopped people going into the park for a "short time", and added that there was no danger to anyone in the park and no animals were on the loose.