Insurers fear pay-out could hit £38 billion

That would make it one of the worst natural disasters - from the insurers' point of view - ever.

The hit to insurers from the New Zealand quake earlier this year is reckoned to be a far more manageable $10 billion.

Experts admitted that it is impossible to predict what insurers will have to pay out with any certainty, but were basing losses on past events.

Barrie Cornes at Panmure Gordon said in a note: "Indications from modellers such as AIR Worldwide suggest that the loss from the earthquake alone could be $35 billion.

"On this basis, we would not be surprised if the total economic loss was north of $100 billion, with the total insured loss being north of $60 billion," he added.

On Friday, before the scope of the nuclear situation emerged, analysts were suggesting a $20 billion hit to the insurers.

Espirito Santo analyst Joy Ferneyhough's did offer a worst-case scenario cost of $50 billion.

The Portuguese bank seemed somewhat confused by this, at first claiming that no such piece of research existed, and later distancing itself from the analysis.

Today the bank says it thinks the losses will be between $15 billion and $20 billion.

Re-insurance shares tumbled again.

Munich Re was off by more than 5%, while Swiss Re and Hanover Re both lost 3%.

Munich said in a statement that due to the "complexity and severity" of the events in Japan, it would take time to say how much it expects to pay out.

The company moved to reassure clients that it has the cash.

"We are very closely committed to our Japanese clients and the country as a whole and will play our part in dealing with the losses," said chief executive Nikolaus von Bomhard. "Munich Re can be relied on, especially in times like these."

Chaucer, the Lloyds of London insurer, told the stockmarket today that it is one "of a panel" of insurers that cover the Tokyo Electric Power Company, the owner of two nuclear sites in the affected area.

It points out that under the Japanese nuclear act of 1961, operators are not liable for damage arising from a "grave natural disaster of an exceptional disaster".

Chaucer says, on this basis, it does not expect "any significant insured loss" to arise.

The insurer's own shares edged up 1.75p to 55.75p.