The spatiotemporal characteristics of infrequent back-arc rifting events, and their relationships to volcanic unrest and other transient processes within the subduction system are not well known. We report 10 spatio-temporal swarms of earthquakes that occurred along ~300 km of the northern and central Taupō Volcanic Zone (TVZ) between March-September 2019. The swarms lack clear mainshock-aftershock distributions, suggesting involvement of magmatic or pressurized fluids. The most energetic swarms occurred beneath the southwestern flank of Whakaari/White Island volcano (WI) and were accompanied by elevated SO2 emissions and ~8 mm southwest displacement of the edifice. Focal mechanisms of the WI swarms suggest horizontal dilation in the direction of tectonic extension achieved by slip along arrays of closely spaced NE-striking normal faults linked by oblique-slip to strike-slip faults. Given the small GNSS displacements, we favor the interpretation that magmatic volatiles were released by changes in crustal stress. Based on the punctuated, cascading nature of swarms along the northern TVZ, we hypothesize that a rapid reduction in the minimum horizontal stress occurred along the entire northern TVZ over ~5 months, leading to widespread unrest. The probable release of magmatic fluids from shallow magma bodies in the vicinity of WI between May and June argues against a causal relation to the December 9, 2019 WI eruption.