Mr Key said the Treasury was doing detailed work on the implications of the earthquake and options for funding recovery.
He warned that the central business district could be closed for months.
The Government is set to announce temporary subsidies today for Christchurch-based businesses that will run into the hundreds of millions of dollars.
He said rebuilding Christchurch could take between five and 10 years and would cost more than $14 billion.
His preference at present was to increase the Earthquake Commission levies paid from household insurance rather than set a general temporary disaster levy, as the Australian government had recently done.
But that could see the EQC component of premiums treble from an average $60 as year to $180 a year.
"The main reason our initial thinking is for an increase in the EQC levy as opposed to an additional levy is because we already have in place that provisioning system, which Australia doesn't."
There was $6.4 billion in EQC reserves before the first earthquake.
It was likely that the first $3 billion to $4 billion costs of the two earthquakes would come from the EQC, $5 billion from reinsurers and at least another $5 billion from private insurance.
On current rates, it would take until 2025 to get the reserves back to $6.4 billion.
"If we triple it, we get there in nine years."
Asked if it would alter the plan to get back to surplus in the 2014-15 year - a year ahead of what had been scheduled in December - Mr Key said that was possible.
"It's too early to tell but the earthquake is of such economic significance that it may challenge that proposition."
Major infrastructure projects on the books at present were being reprioritised although Auckland's Waterview motorway project was not in jeopardy, he said.
In the short term, some businesses would be given help to relocate to other parts of Christchurch.
And the rules around the subsidies given to businesses after the September 4 earthquake are expected to be relaxed.
Generally, they were a $350 a week gross wage subsidy for small businesses with fewer than 20 employees.
Mr Key said the subsidies to be announced today would be for a month and in that time, officials would design other support packages.
"There are so many people who will need to qualify that if we were to go through all the normal testing provisions, it would be very difficult to achieve in the timeframe."
The subsidies would not go to companies, such as banks, that would have the resources to relocate.
Mr Key said the Crown accounts would take a hit in the May Budget - revenues would be down because of the reduced economic activity.
- Audrey Young
