An offshore subsea wellbore activities system and method wherein use is made of a tower and a motion arm assembly with vertical drive adapted to move the motion arm along a vertical motion arm rail relative to the tower. Also use is made of a wellbore activities device comprising a riser tension frame having an upper frame section, a lower frame section provided with a riser attachment device adapted to attach a riser to said lower frame section so as to extend in a firing line, and a vertical riser load bearing structure, e.g. formed by struts. The wellbore activities device further comprises a coiled tubing injector, a wireline lubricator, and one or more pressure control devices associated with the coiled tubing injector and/or the wireline lubricator received by and individually movable within the riser tension frame. The wellbore activities device provides a lateral firing line access passage allowing to transfer an elongated wellbore tool or a wellbore tubular in vertical orientation thereof by means of the motion arm assembly in a substantially lateral motion between and a remote position outside of the riser tension frame and an operative position within the riser tension frame and aligned with the firing line.