The performance of an ANC system largely depends on the availability of an accurate secondary path model. This is however a major challenge in multichannel ANC where the computational complexity increases significantly with the number of secondary sources and error sensors. This paper proposes wave-domain adaptive processing algorithm for multichannel ANC with online secondary modelling to cancel a tonal noise over a region of space within a reverberant room. The design is based on exploiting a special property of the secondary path model in the wave domain. A feedback control system is implemented, where a single microphone array is placed at the boundary of the control region to measure the residual signals, and a loudspeaker array reproduces secondary sources to generate the anti-noise signals and auxiliary noise for secondary path modelling. Through experimental verification in comparison with existing methods the proposed algorithm demonstrates more efficient adaptation with low-level auxiliary noise.