Typhoon Jebi, which struck Japan last September, has become the costliest storm on record for the country due to “loss creep” that has extended into this year, S&P Global Ratings says.

Insured losses from the typhoon are estimated at about $US15 billion ($22.1 billion), up from $US6 billion ($8.8 billion) late last year.

“Although the top 20 global reinsurers will likely be able to manage Jebi’s loss creep, further material developments could yet occur,” the ratings company says.

“Jebi is an important reminder of the significant uncertainty associated with early loss estimates.”

Global reinsurance has remained resilient despite losses from natural catastrophes reaching a record back-to-back high over the past two years.

Some reinsurers are taking advantage of higher premium rates and are increasing exposure to catastrophe risk, which could heighten earnings and capital volatility.

The magnitude of 2018 losses helped push up prices at the April and mid-year renewals, with property catastrophe rates increasing 15-25% on loss-affected accounts, S&P says.

In a separate report, S&P says reinsurers face challenges from mounting cyber losses, with cover often embedded in traditional products as a “non-affirmative silent cyber exposure”.

Gross written premium for cyber cover through separate products or as an additional peril for existing policies was around $US5 billion ($7.4 billion) last year, but could reach $US8 billion ($8.8 billion) by 2022, S&P says.

“We believe the global affirmative cyber insurance market will continue to expand faster than the vast majority of other traditional lines,” it says.

Total economic losses from cybercrime were estimated at $US600 billion ($883.5 billion) last year, highlighting the insurance protection gap, according to the report.