The company said the incident occurred at 8:30pm local time last night in the Kencana underground mine, causing damage to a number of mining levels.
"The Kencana mine was evacuated immediately after the event and all personnel have been accounted for, except for one employee who is believed to be trapped approximately 300m underground," Newcrest said.
The company said the cause of the geotechnical event was unknown, and no other injuries had been reported.
"At this time, our priority is to contact and rescue the trapped employee and provide all support necessary to the employee's family and Gosowong workforce," Newcrest said.
Newcrest said all efforts and specialist resources were being applied to the rescue, and the family and authorities had been notified.
Mining and processing has been suspended.
Kencana is one of two underground mines that make up the Gosowong operation.
The mine is 75%-owned by Newcrest and is set to produce 300,000-350,000 ounces of gold this financial year.
Gosowong employs around 2200 workers, around 98% of which are Indonesian.