Authorities say a third person has died more than a week after a hammer attack in a New York City restaurant.

WABC says the death of restaurant manager Tsz Mat Pung was announced on Thursday.

The attacker walked into the Seaport Buffet in the Sheepshead Bay area of Brooklyn on January 15 and began hitting unsuspecting victims with a hammer, sending people fleeing. Authorities don't believe he had a connection to the restaurant.

The restaurant's chef, 34-year old Fufai Pun, died in the attack. The owner, 60-year-old Kheong Ng-Thang, died three days later.

The alleged attacker remains hospitalised in a psychiatric ward.