The United States military in Hawaii offered their assistance after the 7.1 magnitude earthquake in Canterbury but were turned down because local authorities have the situation under control, Civil Defence director John Hamilton said.
Central Christchurch streets are piled with rubble and cordoned off after the quake, which hit at 4.35am on Saturday. Strong winds and rain forecast for Sunday were seen as possibly causing problems.
Some roads were closed due to liquefaction or flooding and more than 200 residents left their homes and took shelter at three welfare centres set up in the city.
Water supply had resumed for all but 15-20% and electricity was back on in 90% of Christchurch.
A state of emergency would remain until noon on Monday in the city.
Mr Hamilton spoke to media following a top-level briefing at the emergency bunker in Parliament and said officials were impressed with the response from the people of Canterbury.
Checks on the structural integrity of buildings continued yesterday and the exact state of infrastructure remained unclear.
It could be weeks until damaged buildings in central Christchurch were made safe, Mr Hamilton said.
"In some cases overseas, until a building has been rendered safe by demolition, you just have to keep people away," he said.
Drinking water and sewerage systems remained an issue for both city and rural communities.
An update was expected from the Ministry of Education later this afternoon about which schools would open tomorrow.
Most government agencies, including police, were sending in extra staff to relieve those on duty and the army remained on standby to help if needed.
Offers of help had also been made by the United States military in Hawaii and by others through various United Nations programmes, Mr Hamilton said.
"I suppose they're probably surprised that we turned down their offers of assistance because in most cases an earthquake of the magnitude that we've experienced would inevitably result in high casualty numbers and the need for humanitarian assistance.
"We're very grateful that the offers were made and fortunately we were able to say 'not required'."
Senior government ministers would meet to discuss further taxpayer-funded assistance for the people of Canterbury, including how much to help those without insurance.
Prime Minister John Key has pledged government support to the people of Canterbury, where damage has been estimated at $2 billion by the Earthquake Commission.
Mr Key, who visited Christchurch on Saturday, said it looked like a scene out of a movie.
"The roads were just ripped apart. I saw a church completely broken in half," he told TV One's Q and A.
The local authorities and civil defence had done a good job, Mr Key said.