Wanted: Star-crossed lover whose unsigned declaration of ardour has been discovered in an earthquake-damaged observatory.

The Arts Centre of Christchurch, Te Matatiki Toi Ora, is seeking the anonymous author of the love note scrawled on the back of a photo of a woman.

It was found in the centre's 122-year-old stone-tower observatory, where visitors could gaze at the night sky - until the devastating earthquakes struck the city.

Workers deconstructing the attic of the damaged building on Wednesday found the photo alongside two Polaroid images of women breastfeeding infants, an old tobacco tin, an old drawing-pin box and a mummified bird.

The black and white photo of the woman is a close-up of a contemplative face. She has dark hair and possibly hazel eyes, the Arts Centre says. The photo appears to have been printed in December 2006, judging from an imprint on it.

The note on the back says: "This is a picture of the girl I love. Since we both love this country I leave it here and when everything works fine with us both might pick it up and I'll ask her to marry me. Please leave the picture here! Thanks."

Arts Centre chief executive Philip Aldridge said staff would love to reunite the author of the note, who seemed to be from overseas, with the photograph.

"If we're able to return the photo to them, we'll tell them we're sorry we had to remove it, but I'm sure they'll understand why," he said.

"We really hope the author and their girlfriend had a happy ending too, even though the photo hasn't yet been collected."

Access to the observatory was restricted after the city's September 2010 earthquake, and ended with the tower's destruction by the earthquake in February 2011.

Its reconstruction is costing the Arts Centre trust $10 million.

The find is among the more unusual at the Arts Centre, where workers have unearthed a great variety of items since the $290 million, 10-year restoration programme began in 2012.

Notable finds include a large rat skeleton, a terse letter from a man to his ex-wife from the 1970s, a hooded seal jaw, and a boxing glove.

The centre is being progressively reopened to the public. So far 11 of the 23 buildings are open, with the observatory a key part of the second restoration stage.