The Friends of the Koala care centre in northern New South Wales is struggling to keep up with demand as it takes in double the number of koalas hit by vehicles compared to a usual winter.

The centre, based in Lismore, usually takes in about 20 sick and injured koalas for the month of July, but this year admitted 48.

Care co-ordinator Susannah Keogh said half of those had been hit by vehicles.

"We don't expect these kinds of numbers until spring, for this to happen in the middle of winter is highly unusual," she said.

She said 13 of the koalas hit by vehicles had died.

Baby koala Pebbles was taken to the Lismore Koala Care Centre with her mother River after a suspected car strike. ( ABC North Coast: Samantha Turnbull )

"Usually when a koala gets hit by a car, it's almost always fatal because the blow they get is so significant for such a small animal," she said.

"But a couple of them seem to have just been rolled under a car, so they don't have any massive breaks or abrasions.

"Some of them have a little bit of bleeding in the abdomen, or just a head wound we need to keep an eye on for a few weeks."

Ms Keogh believed the rise could be attributed to unseasonably warm weather across the Northern Rivers region.

"Because the weather has been so beautiful, koalas are confused about what time of year it is," she said.

"They think it's spring time so they start moving around, they start mating and claiming territory.

"Unfortunately when they're on the ground that's when they get into trouble. They're moving around a lot more than they usually would at this time of year."

River the koala is believed to have been hit by a car in the Lismore area. ( ABC North Coast: Samantha Turnbull )

Ms Keogh said carers were worried about what the warmer months would bring.

"We are completely booked out, no vacancies," she said.

"It's very possible the movement we're seeing with koalas now will continue in spring and through to summer.

"This is the weather they do love to move around in so it looks like they might be getting into trouble a bit more often.

"We're all a little bit terrified, to be honest, about what's to come.

"Unfortunately it looks like spring just came too early for us this year."

Ms Keogh urged drivers to take extra care, but also urged people to consider volunteering with Friends of the Koala.

"With this high number of koalas coming in we're always looking for people to help out," she said.

"It's the best thing I've ever done in my life."