Wellington is prepared for a big earthquake and the city's response plan isn't going to be changed because of a new report warning utilities could be knocked out for months, Civil Defence Minister Chris Tremain says.

The Wellington Lifelines Group has spent six months looking at what it would take to get essential infrastructure up and running after a 7.5 earthquake.

It says the airport would be operational within hours, and food and water could be shipped in and distributed from the port.

But in many places it could take nearly three months to restore gas, two months to restore power and between one and two months to restore water supplies.

State Highway 1 could take up to four months to fix and slips could close the Rimutaka Hill Road for weeks.

Mr Tremain says Wellington is ready to handle a major earthquake.

"The report is concerning but we've got a response plan which puts us in a good position," he told reporters on Tuesday.

"I think we're ready, there's always room for us to lift our game but I do think we are well prepared."

Asked whether there would be any changes in light of the group's report, he replied: "No. We will keep lifting the bar and looking at what we can do better but at the moment I'm comfortable with the plan."

Greater Wellington chairwoman Fran Wilde says the report makes sober reading.

"The complexities of restoring essential services after a severe earthquake are considerable and the job will not be achieved quickly," she said.

"The findings should make all of us stop and reassess our personal preparedness."