Y. -Z. Cai, A. Pastorello, T. J. Moriya, X. -F. Wang, A. Reguitti, A. V. Filippenko, L. Tomasella, K. Čotar, A. Siviero, N. Elias-Rosa, T. G. Brink, G. Valerin, S. Benetti, J. -W. Zhao, Z. -H. Peng, Z. -Y. Wang, I. Altunin, R. Baer-Way, E. Baron, V. Chander, M. Chu, A. deGraw, J. M. DerKacy, J. Isern, C. Jennings, R. Kotak, L. -P. Li, P. Marziani, M. May, P. A. Mazzali, A. Morales-Garoffolo, S. Moran, P. Ochner, I. Salmaso, L. Tartaglia, M. Turatto, H. -Y. Wu, D. -F. Xiang, S. -Y. Yan, J. -J. Zhang, W. Zheng

We present the photometric and spectroscopic analysis of the luminous and long-lasting Type IIn supernova (SN) 2019vxm. The SN reaches a peak V-band absolute magnitude of MV = -20.01 +/- 0.13 mag in 35.0 days, and displays slow evolution in both the light curves and spectra, resembling that of long-lived SNe IIn. A mid-infrared (MIR) excess is detected starting from seven months after maximum brightness, suggesting a few 10^-3 solar masses of dust are newly formed at >= 210 days (and up to 0.01 solar masses at +4.5 yr). The spectra are dominated by a blue continuum at early stages, with narrow, symmetric Balmer lines and flash-ionisation emission lines of C III, N III, and He II. Comparing our flash-ionised spectrum with early interacting SN spectral models, we estimate a lower limit for the mass-loss rate of the progenitor of >= 0.01 solar masses per year. A weak P Cygni absorption feature is detected in the H-beta profile of the high-resolution Echelle spectrum at +19.7 d, suggesting the presence of slow-moving (60 +/- 10 km/s), unshocked circumstellar material (CSM) arising from the pre-SN wind of the progenitor. The H-alpha and H-beta profiles gradually evolve and become broader and asymmetric, showing a progressively increasing blueshift, with a clear flux deficit in the red wings of the broad velocity component after +102 days. Our observed bolometric light curve before about 100 days can be well fitted by a power-law function (L(t) = 2 x 10^44 (t/day)^-0.49 erg/s), which is very similar to SN 2010jl.