A law requiring earthquake-prone buildings to be identified and upgraded has come into effect this week.

The new regime divides the country into three earthquake categories.

Photo: NZ government

In high-risk areas, such as Wellington, buildings need to be assessed within five years and upgraded within 15 years.

In medium-risk areas such as Hamilton or Nelson, the timeframe is 10 and 25 years respectively, and in low-risk areas such as Auckland it is 15 and 35 years.

There is also flexibility in the regime to add 10 years to the timetable for registered heritage buildings and to exempt buildings with low risk and low usage.

Building and Construction Minister Nick Smith said he was considering assistance for multi-unit complexes where some parties may struggle to raise the finance for their share of strengthening costs.

Wellington apartment owners have pleaded for financial help for those who don't have the money and can't borrow the funds to do the work.

Two representative bodies - Inner City Wellington and the Body Corporate Chairs' Group - last month asked for central and local government to establish a lender of last resort.

"Officials are considering whether we could extend other government housing guarantee products schemes to assist in these circumstances."

Dr Smith said the safety regime was the most ambitious in the world.

"California goes after older buildings - every other country that has seismic risk only attempts to regulate new buildings.

"That is where I'm confident in saying this system that we are putting in place will make New Zealand safer than any other seismically-affected country."