Police are concerned a Chinese student, who went missing north of Auckland on Saturday, may have fallen into the ocean and drowned.

Yue Gui, aged 30, known as "Alice", was last seen at 11pm on Saturday at the Leigh Marine Reserve Faculty, about 80km north of central Auckland, which is operated by Auckland University, a police spokesman said.

Ms Gui's normal routine was to check the ocean temperature on Sunday morning and police feared she may have fallen into the water, he said.

Tidal and weather conditions meant the ocean was rough on Sunday morning, the spokesman said.

Police staff and a helicopter searched the area today and the Wellington-based dive squad would join the search tomorrow.

Anyone who had seen her in the area was asked to come forward.

Ms Gui, a PHD student, was described as being 1.55m tall, of slim build and with dark hair