A charity says New Zealand could be in "serious trouble" if it doesn't act to address the shortage of social housing for older people - with the population of renters over 65 set to triple by 2050.

Christchurch Methodist Mission executive director Jill Hawkey told RNZ’s Checkpoint programme some seniors are finding themselves homeless, amidst the shortage of affordable and secure social housing, and others are left with little money for food and medicine after paying rent.

On Tuesday, the group handed a petition to Parliament signed by more than 3000 people, calling for increased targeted investment in housing for seniors.

Data from the Ministry of Social Development shows that over 55s are the largest demographic on the social housing waitlist, and the number of over 65s on the waitlist has climbed 34% in four years.

Hawkey told Checkpoint that New Zealand was going to have a problem if it did not invest in suitable housing for older people now.

"Within 20 years, the number of older renters that's over 65 years of age, is going to triple.

"At the moment we've got about 138,000 renters aged over 65, and that's going to be 400,000 renters over the next 25 years, so if we don't start doing something about it now, we're going to find ourselves in serious trouble."

There is also the wider issue of the lack of social housing across the board in New Zealand, with social housing making up just 3.8%  of all housing stock, compared with the OECD average of about 7%, she said.

Hawkey said the human impact was showing up as homelessness among older people.

She said that the first person their homeless outreach team housed last year was a woman in her eighties.

"It's not just Christchurch that we're seeing this, we're hearing similar stories from towns and cities throughout the country" she added, noting that they were finding people over 65 on the streets.

In Christchurch, the waitlist for the Wesley Village just kept growing, and the rent pressure was also growing - with the price of a single bedroom unit costing more than $500 for Papanui, she said.

Hawkey said for seniors who were light on supperannuation, the rents could take up all of their pension and there was little money left for food and medical supplies.

She said there was also concern with the lack of suitable, age-friendly housing, pointing to the fact that a lot of new homes built in Christchurch at the moment had a living room downstairs and bedrooms upstairs, which was unsuitable for older people.

The Christchurch Methodist Mission met with Minister for Seniors Casey Costello on Tuesday and Hawkey said that while there was no commitment yet, there was "lots of interest".

She said Costello talked about the need for cross-party support for older people's housing, and that there was no short-term fix.