Crovalimab will be administered at a dose of 1000 mg intravenously (IV) (for participants weighing 40 to <100 kg) or 1500 mg IV (for participants weighing >=100 kg) on Week 1 Day 1. On Week 1 Day 2 and on Weeks 2, 3 and 4, crovalimab will be administered at a dose of 340 mg subcutaneously (SC). On Week 5 and Q4W thereafter, it will be administered at a dose of 680 mg SC (for participants weighing 40 to <100 kg) or 1020 mg SC (for participants weighing >=100 kg). Enrollment of participants weighing <40 kg will be staggered using two weight-based dose confirmation groups (Group 1 participants weighing >=20 kg to <40 kg, followed by Group 2 participants weighing >=5 kg to <20 kg). All participants will receive an initial IV loading dose, which will be followed by SC dosing at either Q2W or Q4W intervals (depending on body weight), until study completion.