One person has died and two people have been hospitalised with listeria in Tauranga, prompting a warning to pregnant women and others at risk.

Authorities are urgently trying to find the source of the dangerous bacteria which can be found in raw fish, processed meat, hummus and many other cold foods.

It is dangerous for newborn or unborn babies, elderly people, or those with poor immunity.

The region's medical officer of health, Neil de Wet, says all three of those who were affected were between 70 and 90 years old.

The person who died already had a terminal condition, he says.

It was possible the cases were linked because it was unusual to see three in two weeks, says Neil.

Usually the region had between one and five cases a year.

An investigation with the Ministry for Primary Industries is under way to find the source.

Its compliance director Gary Orr says they will look to see if there is a common food connection.

"Any case of listeria is a worry for us, particularly if there is a link to food ... If it is shown to have a link to food then we will move very quickly to take that risk food out of the system or alert the public."

Public health officers will interview the patients or their families about where they had been and what they had eaten to see if there is a link.

Pregnant women and other groups vulnerable to the disease should follow the usual advice to avoid risky foods, says Neil.

Rowan Quinn/RNZ.