Parts of New Zealand's second largest city will be abandoned because of last month's earthquake.

Prime Minister John Key said some parts of Christchurch have been so badly damaged, nothing can be rebuilt on the land.

Key added that 10,000 homes and several hundred commercial buildings will have to be demolished.

"We will have to provide other alternatives for people to live in because the land has been so badly damaged," he said. "We can't fix it -- certainly not in a reasonable time frame."

So far, 166 people have been confirmed dead as a result of the 6.3 magnitude quake.

Officials expect the toll to rise to more than 200 as rescuers continue to search for bodies in the rubble.

A national memorial service is planned for March 18.

Key says the open-air service in a city park could attract up to 100,000 people.