After taking the reins at QBE at the start of this month, Mr Regan on Tuesday pointed to natural catastrophes and problems in its emerging markets business and the United States as he unveiled the fourth profit downgrade in a year.

He also flagged broad plans to make QBE a smaller and simpler business, a plan that is tipped to lead to asset sales in its emerging markets division.

After initially falling by about 5 per cent, QBE shares recovered to close 0.6 per cent lower at $10.43, as investors shrugged off the downgrade as a predictable move from a new CEO.

"It's a page out of the new CEO playbook," said Clime Asset Management senior analyst David Walker.

Mr Walker said that as well as re-basing the market's earnings expectations, QBE appeared to be signalling that it would shrink and simplify itself in order to improve performance.

PM Capital's portfolio manager for Australian equities, Uday Cheruvu, also said the downgrade had been anticipated in the market, while welcoming the signs Mr Regan was looking to simplify the business.

"The big issue with QBE is that it's a black box for a lot of investors," Mr Cheruvu said. "The simpler you make it, the easier it is to track and understand what's happening."

QBE warned that due to natural catastrophes including Californian fires and last month's storms in Australia, its combined operating ratio - claims as a share of premium revenue - would blow out to 104 per cent, compared with guidance of 100 per cent to 102 per cent in October.

A ratio above 100 per cent reflects underwriting that is unprofitable.

It also said it would bolster claims reserves by $US110 million, and flagged various smaller items that would further undermine earnings, including weather-related claims and higher than expected costs.

QBE also said it would write down the goodwill in its North American operations, flagging a $US700 million impairment charge to the carrying value of this business. It said President Trump's corporate tax cuts had triggered a $US230 million write-down in the value of deferred tax assets in its North American business.

Growing investor frustration over the dissapointng results led to former chief executive John Neal announcing he would step down in October, to be replaced by Mr Regan, who was previously chief financial officer.

Mr Regan said natural catastrophes of the last year were "pretty much unprecedented" for insurance companies, with the industry had experienced a series of "medium sized" natural catastrophes, which tended to have a bigger impact on profits than one very large natural disaster.

Even so, Mr Regan also conceed the company also needed to lift its game in underwriting, and become more efficient.

"We need to simplify the group somewhat and reduce risk," he told investors on a conference call. "You should expect that QBE going forward is smaller, more focused, and a little bit less complex than QBE today."

Bell Potter analyst TS Lim said investors were giving QBE "the benefit of the doubt," and banking on the board holding the dividend and keeping in place a share buyback announced last year.

"The numbers suggest they should be able to maintain the buyback, and they don't need to cut the dividend," Mr Lim said.

Morningstar senior equities analyst David Ellis said he was frustrated with series of downgrades, questioning why QBE had not taken the writedown on its American business earlier, given it has been working closely on this business for several years.

"I'm frustrated. It's very common for new CEOs to clear the decks, but we've had three or four years of this from QBE and this is just one more example."