An emergency casing packoff assembly (170) that is adapted to be installed in a wellhead (100) through a blowout preventer includes an upper packoff body (171), a lower packoff body (174) releasably coupled to the upper packoff body (171), and a metal seal ring (175) that is adapted to create a metal to metal seal between the packoff assembly (170) and a casing (110) supported in a wellhead (100) when a pressure thrust load is imposed on the packoff assembly (170). The casing packoff assembly (170) further includes a lock ring energizing mandrel (173) threadably coupled to the upper packoff body (171), wherein at least a portion of the lock ring energizing mandrel (173) is adapted to be threadably rotated relative to the upper packoff body (171) so as to lock the packoff assembly (170) into the wellhead (100) while the imposed pressure thrust load is maintained on the packoff assembly (170).