The Christchurch City Mission says some people sleeping rough are refusing emergency accommodation, despite freezing temperatures.

Snow and sleet hit the lower North and the South Island on Tuesday.

In Christchurch, the city mission worried that those sleeping outside could still be wet when temperatures dropped below zero.

Missioner Corinne Haines said it could not force people to accept help.

She said many experiencing homelessness had a bad experience, been through trauma, struggled with their mental health, feared for their safety, or did not trust support services.

"When you're cold, when you're wet, when you're hungry, when you're not quite in step with society, it's very hard to make good and brave decisions, and for some of these people, leaving the street is actually a very brave decision," Haines said.

In a Facebook post, the city mission said staff were genuinely worried they would find someone who had not survived through the night.

"That is especially so because we are seeing more elderly people now out on the streets. They came across an 82-year-old last week who, for his own reasons, chose to stay out."

Haines said it was working to build trust.

"We meet them where they are. We check in with them after a cold night or severe weather. We bring practical support for them.

"That's not ideal from our perspective. We would much sooner they came inside, and they took up our offer of support, of housing, even if it's only short-term.

"But if we can meet them where they are, if we can give them food, we can give the blankets, socks, hygiene supplies, sleeping bags, wet weather gear, then we are showing that we care about them, that we want to help them, and we don't judge them.

"We just keep walking beside them in the hope that one day they will take that step."