UPDATED 3.10pm: The general manager of a storage facility where a woman was stuck in a lift for fourteen hours overnight is investigating exactly how it happened.

The alarm was raised when a customer at Guardian Self Storage in Silverdale north of Auckland heard a woman screaming this morning.

He called 111 and the woman, whose sister rents a storage unit there, was rescued by the Fire Service.

Guardian Self Storage GM Terry King said he's spoken to the woman, who's shaken up but uninjured.

He thinks the bell in the lift did not call the security company, which attends if someone gets stuck.

"The lift basically just stopped. We own five facilities and four have got lifts in them and what would usually happen is that there is an alarm system and you push a button if the lift stops.. And it goes through to a security company and the security company come and obviously over ride the system and get you out.

"In this case for some reason the alarm hasn't gone through to the security company so no one has actually known that [the woman] was in the lift until someone this morning found her."

King said another customer had found the woman.

Terry King said the lift was serviced last week.

He said he's going to do a full examination of what happened.