A massive recovery operation in Christchurch is aimed at making it the most "earthquake-safe" city in the world, its Mayor Bob Parker says.

Prime Minister John Key this morning announced a new stand-alone authority - the Canterbury Earthquake Recovery Authority (CERA) - to lead the earthquake recovery in Christchurch.

The body will have wide-ranging powers to lead and co-ordinate work to rebuild the city.

Mr Parker has hailed the announcement, saying it will allow for the right mix of Government, council and resident involvement.

It is an important part of an overarching effort to make sure Christchurch will never again be devastated by an earthquake, he says.

"Given the scale of the tragedy and the multi-billion dollar cost involved in repairing and rebuilding our city, it is important that we work on this huge task in a partnership with the Government.

"Our ultimate goal is to build the most earthquake-safe city in the world."

CERA will have a life-span of five years and its operations will be reviewed annually.

Its interim chief executive will be Deputy State Services Commissioner John Ombler.

Mr Key says the rebuilding in Christchurch will be a long and complex task which will require huge resources.

It is vital to move forward with business recovery and getting vital infrastructure running, he says.

An Order in Council will have to be made to establish the new body, and that's due to happen within weeks.

Mr Parker says his council will be also working with Government over the next nine months on a plan to rebuild the earthquake-devastated Christchurch city centre.

However, he conceded it would be next year before any significant construction could begin.

"We need to be upfront and say it is unlikely that the significant rebuild of the central city could start before the end of the year. The timeframe of course depends on the Earthquake Commission and the insurance companies completing their work with the property owners.

Government asistance packages to be scaled back

Meanwhile, the Government announced yesterday that assistance packages for Christchurch businesses and workers would be extended, but that the schemes would be scaled back.

Both the Earthquake Support Subsidy for employers and the job loss cover for workers will be extended until April 18, followed by a second round of assistance with tighter application criteria.

Businesses that qualified for the second round would receive payments at gradually reducing rates each fortnight over a six-week period.

Labour's Canterbury Earthquake Recovery spokesperson Clayton Cosgrove told Radio New Zealand this morning that it was too soon to scale back the packages.

"This is not business as usual, you can't just say 'well after 12 weeks everybody's okay and if you're not tough luck'," Mr Cosgove said.

"If a business hasn't got access and nothing has changed for that business no one can say whether it can restart or not, so the Government's answer is 'you're chopped'."

Mr Cosgrove said putting a stop to funding meant there would be premature redundancies and taxpayers would end up paying for welfare for those people.