The search continues for a diver missing off Canterbury's Banks Peninsula.

Police say a 42-year-old man was expected to surface at 9:45am today but after failing to do so, authorities were alerted at around 10am.

The search is at a top Akaroa diving spot where until 3pm today, a helicopter and up to eight boats searched the area between Damon's Bay and Flea Bay.

The New Zealand Police Dive Squad will continue the search this afternoon.

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"All we have at the moment is that police were notified this morning of a possible missing diver in the area of Damon's Bay and Flea Bay, near Banks Peninsula," a police spokeswoman said.

"There is a search involving the Coastguard and a rescue helicopter."