We consider downlink multicast beamforming in a massive MIMO multi-cell network. Aiming at maximizing the minimum SINR among users, for both non-cooperative and cooperative multicasting, we propose a multicast beamforming scheme based on weighted maximum ratio transmission (MRT), and transform the beamforming optimization problem into a weight optimization problem that is solved via the semi-definite relaxation (SDR) approach. The proposed method has a low computational complexity which does not grow with the number of antennas, and thus is suitable for massive MIMO systems. Simulation shows that our proposed multicast beamforming solution yields comparable or better performance than existing approaches but with significantly lower complexity for practical systems with a large but finite number of antennas.