Wellington Central MP Grant Robertson says he will make an example of any landlords found to be illegally raising their rents to exploit students.

Photo: RNZ / Rebekah Parsons-King

From 1 January, the cap on student allowance and living cost loans rose by $50, a Labour election campaign promise.

Since then some students have complained of landlords raising rents to an unreasonable level in response.

Rental prices in Wellington for December were up $30 on October's figures, according to Trade Me numbers.

Its Property Rental Index showed the median price had risen from $450 to $480 since October, peaking back up to match the record set last January.

Overall the city's rental prices rose 6.7 percent in the year, compared to 2.2 percent nationally.

Mr Robertson invited students to get in touch if they believed a landlord was raising rents illegally, and within 10 hours, he said, he had received dozens of reports.

"There are rules in the residential tenancies act about not putting rent up above the market rate, and we are looking very closely at some of the examples that have been put to us today to see if they would breach that act.

"It appears some landlords are taking advantage of people in a very tight rental market ... it feels like this is a bit of exploitation of some pretty vulnerable groups of people."

He said the squeeze on renters was worse than it was at this time last year, and he wanted landlords to be fair and reasonable when considering rent increases.

"Most landlords do a really good job. Those that don't, we're going to call them out."