New Zealand's second largest city, Christchurch, was extensively damaged and emergency was declared early Saturday, after a massive 7.1-magnitude earthquake hit the city causing widespread damage.

Buildings were destroyed, infrastructure including water and sewage pipes damaged, and people injured in the quake, which struck 40km west of Christchurch at 4.35am.

Christchurch residents said the walls of their homes "wobbled like jelly" when the earthquake rocked the city.

Christchurch Mayor Bob Parker has requested the army to help provide safety and security in the city in the wake of the country's most damaging earthquake since the 1931 Napier disaster.

Parker said he requested Prime Minister John Key ask the army to maintain safety and security and help the police over the next 24 hours, Stuff.co.nz reports.

The cost of the cleanup could run into billions of dollars, Prime Minister John Key said.

Key told reporters upon arrival in Christchurch this afternoon that he had seen the damage from the air and it was extensive.

"It will be some time before we know the full extent of the damage but the early indications are it could run into the billions of dollars," Key said.

Meanwhile, one person has died of a heart attack, suffered during the earthquake, an emergency doctor in Christchurch said.

There are four Urban Search and Rescue Teams in New Zealand - two of which were being flown in on airforce planes from Auckland and Palmerston North to Christchurch today. The teams included dogs that could search for people stuck in rubble. (ANI)