Police say plans to expand the rugby fan zone in downtown Auckland allow for a bigger crowd than would be safe.
The police also told a special hearing on Thursday they have doubts organisers of the fan zone could find the necessary number of private security guards.
The Rugby World Cup Authority is considering the urgent expansion of the waterfront zone, after serious overcrowding on the Cup opening night.
Sergeant Gavin Campbell says the licenced area on Captain Cook Wharf should be open to only 8000 fans, not the 10,000 sought by the Government and Auckland Council agencies.
The authority is now considering its recommendations, which have to then be approved by Rugby World Cup Minister Murray McCully.
Facilities are already in place on Captain Cook Wharf in anticipation of the green light being given to expanding the fan zone if needed, from Friday night.