Queen Elizabeth II, New Zealand's head of state, said she was "deeply saddened" by the attacks on two mosques on Friday which left 49 people dead.
"I have been deeply saddened by the appalling events in Christchurch... At this tragic time, my thoughts and prayers are with all New Zealanders," she said in a message.
"Prince Philip and I send our condolences to the families and friends of those who have lost their lives," she said, paying tribute to emergency workers and volunteers providing support to the injured.
Queen Elizabeth, 92, the world's oldest and longest-serving living monarch, is queen of 15 other realms besides Britain, including Australia, Canada and New Zealand.
She last visited New Zealand in 2002 as part of celebrations to mark the 50th anniversary of her accession to the throne.