Key Points:

The Reserve Bank has approved the purchase of billions of dollars worth of residential mortgage-backed securities from two major banks as security should they run short of money.

The central bank has agreed to accept $8.7 billion of housing loans from the ANZ National and Westpac banks as security.

The banks are the first to take up the Reserve Bank's offer to provide extra liquidity during the global financial crisis, Radio New Zealand reported.

Westpac said it has not drawn on the facility yet but might if market conditions remained difficult.

Banking analyst David Tripe said other banks including ASB and BNZ were working on a similar arrangement.