A sales assistant locked herself in a show home bathroom to escape a knife-wielding intruder from sexually attacking her.

The 51-year-old woman was waiting for a client at the show home in the Karaka Lakes development in Papakura, on the southern outskirts of metropolitan Auckland, about 2pm on Friday when the offender tried to force her to have sex with him.

But she locked herself in the bathroom and called 111.

Police described the offender as Maori, aged in his late teens or early 20s, of slim build and medium height. He was clean-shaven and had a tribal tattoo on his left bicep.

He was wearing black leggings, a black t-shirt and motorcycle boots.

Anyone with information is asked to call police.