Wellbore drilling system comprising: a drilling tower, a drill floor having a well center through which a drill string passes along a firing line, a drilling tubulars storage rack adapted to store multiple drilling tubulars in vertical orientation, a tubular racking device having at least a lower first tubular racker assembly and at least a second tubular racker assembly operable at a greater height than the first tubular racker assembly, each tubular racker assembly comprises a base, a motion arm connected to said base, and a tubular gripper member connected or connectable to the motion arm and adapted to grip a tubular, wherein—with the tubular gripping member connected to the motion arm of the racker assemblies—the tubular racking device is adapted to grip and retain a drilling tubular by the tubular racker assemblies, and wherein the tubular racking device is adapted to place a tubular in and remove a tubular from the drilling tubulars storage rack, and wherein the tubular racking device has a reach at least allowing to transfer a tubular gripped by said first and second tubular racker assemblies between the drilling tubulars storage rack and a position of the tubular aligned with the firing line above the well center so as to allow for building and disassembly of a tubulars string, wherein the system further comprises one or more well center tools, each adapted for operation above the well center of the drill floor, wherein the motion arm of the lower first tubular racker assembly is provided with a connector, and the at least one well center tool is provided with a complementary connector, and wherein—with the at least one well center tool connected to the motion arm of the lower tubular racker assembly—the well center tool is operable above the drill floor.