Mayors across the country are urging the Government to set up a formal inquiry into New Zealand banks closing branches in provincial communities.

Kiwibank is set to close seven of its branches over the next year, as more customers moving online to do their banking.

BNZ plans to close 38 branches.

South Wairarapa Mayor Alex Beijen, who wrote the letter and has rallied the support of others across the country, told Mike Hosking his district had experienced a "full withdrawal" of banking branches.

"An area of nearly 3000 sq/km without a single bank," he said.

Beijen is expected to pass the letter to a minister at a meeting at the Beehive this week.

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