"It is an immense sadness that we all feel right now," writes the zoo at 1 p.m. on Friday.
At the same time, they state that they are working intensively to ensure the health of the remaining chimpanzees.
Three of them: Maria-Magdalena, Tjobbe and Selma, have received food.
But the zookeepers have still not managed to get the chimpanzees back into the enclosure.
Two chimpanzees lie still in the house, one of which is confirmed dead.
It involves either Santino and Manda, two well-known and well-liked chimpanzees.
Santino has lived a long time at the zoo and is known for painting pictures.
"These chimpanzees are very much loved and what happened is terrible," writes the zoo.