Shares in Irish banks surged Sept. 30 after the government issued a sweeping guarantee to insure deposits and bank borrowings against a potential collapse.

The government unveiled an unlimited guarantee on deposits at six banks one day after the Irish Stock Exchange suffered its greatest fall in history — and rumors spread that millionaire depositors were withdrawing their savings from Irish institutions.

Finance Minister Brian Lenihan said all deposits in Ireland's six domestically owned banks would be guaranteed by taxpayers in the event that any bank neared insolvency. The guarantee does not apply to foreign-owned banks operating in Ireland because those banks are subject to their parent nation's regulations.

The step raised a week-old government promise to insure the first ¥100,000 ($145,000) in deposits. It followed a record-setting 12.7 percent drop in the Irish Stock Exchange on Sept. 29.

The Sept. 30 guarantee also applies to all of a bank's debts to other institutions worldwide, so if the bank cannot pay its creditors, the Irish taxpayer would cover the bill.