DENVER -- The Denver Zoo closed abruptly Tuesday afternoon after police said someone threatened to crash an airplane into the facility.
Clost to 1,000 guests and staff were evacuated from the grounds just after 3 p.m.
"We immediately contacted Denver police and other government agencies, initiated an evacuation of all guests and staff on the premises and moved animals to safety," the zoo said in a statement.
"Denver police quickly responded to help secure the grounds and investigate the threat."
A number of roads around the zoo were closed to traffic after the large response from the police and fire departments.
Police investigated the situation but said the threat was not deemed to be credible.
No incident occurred and the evacuation was precautionary, according to a zoo spokesman.
"Our top priority is the safety and comfort of our guests, staff and animals," zoo officials said. "We take every threat very seriously and consistently review and practice our procedures to maintain the utmost safety standards."
Police reopened roads around the zoo at about 5:15 p.m.
The zoo will reopen as usual at 9 a.m. Wednesday.