Worksafe NZ, which is investigating the incident, told The Press that the collapse took place at the weekend when no one was underground.
The event was reported to this authority on Monday with a local Reefton resident saying mining had not resumed since.
The small thermal coal mine was shut down by its previous owner Solid Energy in 2009 with only 16 staff impacted by the closure.
Privately owned Crusader was formed in 2010 to acquire and re-open Terrace with hydro-mining starting in 2013.
At the time, the operation was aiming to produce 70,000 tons per annum from an estimated resource of 2Mt over a 15-year life expectancy.