CHRISTCHURCH, New Zealand—Reinsurers will cover the bulk of private-market losses that experts say could have been worse if strict building codes had not been in place when an earthquake struck New Zealand's South Island.

Catastrophe modeling companies say insured losses could range as high as $4.5 billion from the 7.0 quake that rattled the Canterbury region that includes Christchurch, a city of around 350,000. No fatalities were caused by the quake on Sept. 4, another benefit of building codes designed to protect property and lives in the seismically active region, sources said.

“Building codes are created to save lives,” said Imelda Powers, a Philadelphia-based manager in Towers Watson & Co.'s catastrophe management group and a senior consultant in its reinsurance business. “That's their primary objective, and they achieved their objective wonderfully,” she said of the New Zealand codes.

Other experts agreed that the stringent codes saved lives and prevented quake damage from being worse.

“The existence of strict building codes was absolutely the No. 1 factor in limiting damage in this earthquake,” said Kate Stillwell, earthquake product manager at EQECAT Inc. in Oakland, Calif.

“In some ways, they exceed the codes in California,” Jayanta Guin, senior vp of research and modeling at AIR Worldwide Corp. in Boston, said of the New Zealand's codes. “That's how good they are.”

Most of the quake claims from homeowners will be paid by New Zealand's government-sponsored Earthquake Commission. The commission provides coverage of up to $100,000 New Zealand ($72,000) for dwellings and a maximum of $20,000 New Zealand ($14,420) for personal belongings.

As of late last week, the commission said it had received around 39,000 claims and estimates that it will pay around $1 billion New Zealand ($720.9 million) in claims from around 100,000 policyholders. Moody's Investors Service said the commission has $5.6 billion New Zealand ($4.04 billion) to cover claims.

The remaining insured losses are covered by private insurers and reinsured heavily in the global reinsurance market.

Australian insurers are well-protected by reinsurance and should see little impact from quake losses, according to Fitch Australia Pty. Ltd., a Sydney-based unit of Fitch Ratings in New York.

Fitch pointed out that claims are expected to be significant for Insurance Australia Group Ltd. and Suncorp-Metway Ltd., insurers based in Australia that combined hold about 60% of the New Zealand property market. The insurers' net exposures, though, are low, Fitch pointed out.

Suncorp said in a statement that its losses above $60 million New Zealand ($43.3 million) will be covered by reinsurance. Insurance Australia said “the entire event will be covered by our reinsurance arrangements.”

Moody's Investors Service said “although a major event, the impact of the Christchurch quake on the bottom lines of IAG and Suncorp is easily manageable.”

The two largest global reinsurers, Swiss Reinsurance Co. and Munich Reinsurance Co., last week said it was too soon to estimate their losses from the quake or comment on how those claims could affect rates.

However, sources said the cost of reinsurance on New Zealand property risks is expected to rise, which means insurers will be passing their costs along to policyholders.

“I would emphasize that, from our view, because this damage is from an earthquake along a previously unknown fault, it will likely cause an increase in costs for insuring quakes in New Zealand,” Ms. Powers said. “If reinsurance costs increase, they will be passed along to property owners.”

The earthquake in New Zealand, which comes after the Chilean earthquake this year and the Haiti earthquake that caused widespread death but very low insured losses, are reminders of the earthquake peril, said Dominic Christian, deputy CEO of Aon Benfield in London. Together, these events will cause insurers to re-examine the exposure, he said.

“I don't think the earthquake policy form will be reconsidered (as a result of the New Zealand earthquake), but quake risk will get more attention” from underwriters as a result of so much recent seismic activity, Mr. Christian said.

Aon Benfield is the reinsurance broker for the Earthquake Commission.

Catastrophe modeling company Risk Management Solutions Inc. said it expects as much as 70% of the insured loss will come from personal lines policyholders, with the rest from commercial and industrial policyholders.

Christchurch's port is among the commercial operations with damage from the quake. Lyttelton Port Co. Ltd., which operates the port, said the port sustained “significant damage” from the quake but shipping operations were fully operational two days later.

“The cost to repair the damage to the port is likely to be tens of millions of dollars,” Peter Davie, chief executive of the port company, said in a statement.

Some of Christchurch's historic buildings were constructed well before the region's stringent business codes were put in place, which left them more vulnerable to damage.

The Christchurch City Council said the seven-story 104-year-old New Zealand Express Co. building and the 133-year-old Cecil House were so badly damaged by the quake that they would have to be demolished.

Mr. Guin pointed out that New Zealand's building codes call for retrofitting historic buildings to withstand seismic activity, but the requirements are not always enforced. “That's why older buildings are often not upgraded,” he said.

While strong building codes helped save lives, the early hour of the earthquake also was a factor, Mr. Guin said. Residences in the area are mostly wood-frame construction, he said, which withstood the quake better than the old masonry buildings housing retail operations and small businesses in Christchurch.

Had the quake occurred during the day when the city was busy with shoppers, the outcome could have been very different, Mr. Guin said.

Sarah Veysey contributed to this report.