Tower NZ has bought more reinsurance to cover another natural catastrophe event.

This means it now has cover for two more events occurring before September 30.

Tower NZ CEO Rob Flannagan says the move comes after the company decided to treat the June 13 Christchurch aftershock as an event for reinsurance.

The excess on the two events that have occurred in Tower’s 2011 financial year has been put at $NZ5 million ($19.3 million) before tax by the company.

The reinsurance excess on a third potential event will be $NZ2 million ($1.5 million) and a fourth event will be up to $NZ7 million ($5.4 million).

Mr Flannagan says the aggregated cost of the February 22 earthquake and June aftershock will push up the insurer’s expenses for the current financial year.

He now expects expenses to increase by between $NZ22 million ($16.9 million) to $NZ26 million ($20 million) after tax.

But this is now a lower estimate of increased costs for the year compared to previous announcements earlier in the year and last month.