Briscoes storeman Nick Bagnall said more than one horsefloat was filled with cannabis plants in pots during the morning. Police were also seen carrying out large rubbish bags.
The growing operation was substantial, professional and well set out, with automatic systems for watering, ventilation and fertiliser, and a lighting system with timers, he said.
One man has been charged with possession of cannabis for supply and cultivating cannabis. Mr Kirby would not give his occupation. He will appear in Wanganui District Court on Tuesday.
No one else has been charged, but inquiries are continuing.
There were people living in part of the building, but it was yet to be determined whether they were involved.
The Beijing Restaurant building has been for sale for some time. It is listed on Trade Me at $570,000.
Mr Kirby said police had found indoor cannabis-growing operations in houses, garages, sheds and industrial buildings, but it was rare to find one in the middle of town in a commercial building.
The restaurant remained closed last night.
