Police spokesman Kevin Loughlin said the two 16-year-olds were armed with knives when they entered the Vipond Dairy on the Whangaporoa Peninsula about 12.30pm yesterday.

Wearing disguises, one youth remained at the entrance to the shop while the other went to the counter, threatened the Korean dairy owner with the knife and demanded cash.

The owner chased both of them out of his store and the two offenders left the store empty handed, he said.

As they ran from the store, a security guard who had earlier seen them action suspiciously, sprang into action.

"He caught, disarmed and held them until the police arrived," Mr Loughlin said.

Both youths were due to appear in North Shore District Court tomorrow, charged with assault with intent to rob, the maximum penalty for which is 14 years