Police are asking the public for help finding a missing woman in the Waikato region.

Finnesse Endonia Kairau, 41, has not been seen since leaving the Waikato Hospital with her sister yesterday and there were concerns for her safety, Senior Sergeant Juliet Burgess said.

Kairau had been admitted to hospital on Monday and police said attempts to contact her family since her disappearance had been unsuccessful.

"We believe family members of Finnesse have assisted in her leaving the centre without the centre's permission," said Sergeant Burgess.

Finnesse was last seen wearing a black polar fleece sweatshirt and blue jeans.

She was described as a fair skinned Maori woman, of thin build with long black hair.