He said the ED was running at near full capacity as it was.
"By us bringing in a lot more patients they're going to get stretched, and that means there won't be room for people who have real emergencies."
Keenan said paramedics were expecting the demographic of people pouring into Wellington would most likely be wealthy, middle aged rugby patrons.
"I think the intoxicated people are the least of our problems.
"We'll have people falling over and having traumatic injuries, we'll have people who become unwell as a result of their normal medication."
Keenan said 30 extra paramedics would be on board to help out and a command centre would be set up.
He said the street hospitals would have ambulances and tents to treat people in.
Wellington City Council Events portfolio leader Paul Eagle said the street hospitals would help the city run more smoothly.
"Great initiative from the Wellington Free Ambulance, what we'll have is a service for those who come home from the games and if they need help, then they've got instant help right there."
Keenan said closures would make it more challenging to get people to Wellington Hospital if they could not be treated on the street.
Eagle said people should not get behind the wheel on game nights unless they had to, so traffic could still run smoothly.
"What we're saying to people is catch public transport, make sure you walk to the game from the inner city rather than try and get a park at the gate, which is the typical Kiwi thing."
Keenan said staff would also be keeping a close eye on campervans.
"There will be a level of surveillance happening so if we get called out to a park that's got a lot of motor homes in it and there has been an outbreak of diarrhoea and vomiting, then we'll be able to get that information to the public health services and deal with that."
Last month the Wellington Region Economic Agency said it was about 100 camping sites short of the 1300 needed to cater for those travelling the country in campervans.
Partnerships and events general manager Warrick Dent said campervans could overflow into Oriental Prd, Kent Tce and Cambridge Tce if needed.