"Despite being awarded several times this year for our continued focus on safety, this incident has really knocked us off balance," CEO Scott Perry said on a call Monday.

"Our primary concern is to safely return our two missing employees and the safety of our search and rescue teams. We are coordinating closely with family members of the missing team members and local authorities."

Centerra said Sunday the Kumtor mine experienced a "significant rock movement" at the Lysii waste rock dump early in the day.

Mining has been halted indefinitely while the company reworks the mine plan, since all the waste rock from mining was scheduled to be placed on the compromised facility.

The Lysii valley is over a ridge to the north of the vast open pit and is not impacting the stability of the pit nor any of its infrastructure, according to the company.

Perry said company engineers were working on an alternative waste dumping plan for Kumtor that could use the waste dumps in the central valley, in the Sarytor valley or in-pit waste dumping. A revised waste dumping strategy is being developed.

While no other infrastructure was impacted, Perry said the company was building a secondary water pipeline to by-pass any possible impact to the main water supply at the bottom of the Lysii valley.

Perry does not foresee any adjustment to the 2019 production guidance, with Kumtor production for 2020 being largely "de-risked", he said.

"We've been able to stockpile all inventory required for 2020 production. The gold production profile is already de-risked," he said.

"The board has not approved the budget for 2020 and thus I cannot release guidance yet, but we're expecting normal course production levels to the end of 2020."

Following the search and rescue effort, the company's attention will turn to an "exhaustive investigation" into the cause of the rock slide.

Centerra in October increased its 2019 consolidated gold guidance to 730,000-765,000oz, reflecting an increase in expected Kumtor ounces to 575,000-590,000oz.