Reported insured losses from the Tianjin, China, port explosions have already passed early estimates of $1.5 billion, and global insurers and reinsurers are uncertain how much higher the losses may go.

At least 18 reinsurers reported large losses from the mid-August disaster in their third-quarter financial statements, many related to the massive destruction of automobiles stored in the port at the time of the blasts.

Insured losses are expected to fall largely on Chinese insurers and their reinsurers, multinationals' global property programs and marine cargo underwriters, market sources say.

Much is still unknown about the losses, including the extent of supply chain disruptions, damage to containerized and bulk cargo, and pollution or contamination claims.

“Significant uncertainties remain, especially regarding business interruption/contingent business interruption losses and regarding contaminated vehicles,” said a spokesman for Swiss Re Ltd., which reported $250 million in Tianjin-related losses as of Sept. 30. “These factors could significantly swing the estimate in either direction.”

“It's difficult to know what's ahead,” said Craig Neame, a partner at Holman Fenwick Willan L.L.P. in London. “We're at a very early stage of working out the losses and where they are going to fall.”

Tianjin, one of the world's busiest container ports, also handles a large part of China's auto imports and is a major transshipment point to Beijing and northeastern China.

On Aug. 12, two blasts tore through a chemical warehouse owned by Tianjin Dongjiang Port Rui Hai International Logistics Co. Ltd., killing 173 people and injuring more than 700. The warehouse contained 3,000 tons of hazardous chemicals, including 700 tons of toxic sodium cyanide and 800 tons of explosive ammonium nitrate, according to state-controlled China Daily.

Along with destroying or damaging buildings and infrastructure within a 1.2-mile radius, the blasts and ensuing fire destroyed thousands of stacked cargo containers and incinerated more than 10,000 new cars, according to news reports.

Chinese authorities in August announced investigations of more than a dozen people — including Tianjin port and governmental officials and two owners of Rui Hai International — alleging that Rui Hai was allowed to operate illegally in violation of chemical storage safety rules, China Daily reported.

Early loss estimates have varied.

Chicago-based Fitch Ratings Inc. predicted up to $1.5 billion in losses for Chinese property/casualty companies, while reinsurance broker Guy Carpenter & Co. L.L.C. estimated overall insured losses of $1.6 billion to $3.3 billion.

Much of the reported damage so far has been to cars.

Jaguar Land Rover Automotive P.L.C. lost many of the 5,800 vehicles being stored at the port, Mumbai, India-based parent Tata Motors Ltd. reported. Wolfsburg, Germany-based Volkswagen A.G. reported more than 2,700 cars damaged, while Amsterdam-based Fiat Chrysler Automobiles N.V. took a $155 million third-quarter write-down for damaged vehicles. Other importers with losses include Seoul, South Korea-based Hyundai Motor Co. and Boulogne-Billancourt, France-based Renault Group.

A spokesman for Zurich Insurance Group Ltd., which reported $275 million in Tianjin property and marine losses, said most related to eight auto industry policyholders.

Several auto manufacturers have diverted shipments to other Chinese ports, and any delay in delivery of cars and parts within China could lead to contingent BI claims, Mr. Neame said.

While scores of multinational companies have offices or operations in Tianjin — and while some, including Toyota Motor Corp. and Honeywell International Inc., reported brief plant closures — few have disclosed the disaster's financial effects so far.

Vishay Intertechnology Inc., a Malvern, Pennsylvania-based electronics manufacturer with $560 million in sales as of Sept. 30, said it suffered $9.6 million in damages to its Tianjin plant — $4.3 million of which it expects to recover from insurers — and $20 million in lost revenue. A company spokesman could not be reached for comment.

Chemtura Corp., a Middlebury, Connecticut-based specialty chemical maker, said it “saw some supply chain disruption” in Tianjin imports and exports, but did not quantify any losses, according to its third-quarter report.

Chinese chemical exporters could face delays moving products into and out of Tianjin, particularly if port officials enforce more stringent safety rules. But it's uncertain to what extent any resulting business interruption or contingent business interruption losses are insured, Mr. Neame said.

Meanwhile, the U.S. Food and Drug Administration has increased surveillance of FDA-regulated products shipped to the U.S. from Tianjin on or after Aug. 12, requiring shippers to provide additional safety information and potentially creating supply chain problems for importers, market sources said.

Overall, the complex Tianjin loss has left insurers and reinsurers uncertain about the ultimate extent of covered damages nearly two months after the disaster. In third-quarter financial filings, most underwriters have noted that their reported losses are preliminary estimates still subject to revisions.

Zurich's $275 million loss “represents Zurich's best estimate,” its spokesman said. “The nature of many of the (Tianjin) losses and the extended remediation period to complete repairs means that uncertainty as to the final cost remains.”