Rents may have inched higher for the 23rd month in a row, but a lack of new deals and a large number of landlord concessions hint at an impending market slowdown.

Median rental prices in Manhattan increased by 1.5 percent last month — from Jan. 2015 — to $3,350, continuing a near two-year trend of year-over-year increases, according to Douglas Elliman’s latest rental market report. But the outlook isn’t exactly rosy: Vacancy rates are high, new leases are down and landlords are making a lot of concessions.

“We’re clearly seeing a slowdown,” said Jonathan Miller, president of Miller Samuel and author of the Elliman report. “Really, what is happening is this combination of affordability being tested because rents can’t rise forever, and the new product entering the market is generally skewed toward the luxury market.”

Vacancy rates hit the second highest rate in nine years at 2.82 percent. January saw 3,373 new leases, a whopping 19.8 percent drop from the same time last year. The decrease can be attributed to the success of landlords in convincing tenants to renew their leases, as well as high rents that drove tenants to the outer boroughs, Miller said.

The number of rentals with concessions reached 16.4 percent, which is nearly twice the five-year average. He said rent rates are likely to “bump along a high plateau” for some time before rents start to drop.

“We’re just in this transition period, and the market is trying to find its way,” Miller said. “But I don’t see big savings ahead for consumers. Anything that happens will be in slow-motion.”

Another report by Citi Habitats found that 17 percent of the brokerage’s rental transactions offered tenants a free month’s rent and/or payment of the broker fee, a 7 percent increase from January 2015. Gary Malin, president of Citi Habitats, said that the concessions have helped offset high rents and stabilize the market.

“The market is still strong. It’s just gotten a little too frothy for some people,” he said.

The trend is less pronounced in Brooklyn and Queens. Median rent hit $2,923 in Brooklyn last month, a .8 percent increase from December 2015 and a .8 percent year-over-year increase. The slight jump is a modest one, but follows two months with no year-over-year growth, according to the Elliman report.

Median rent in Queens fell to $2,767, a 4.8 percent year-over-year decrease. New leases in the borough jumped 53.1 percent from January 2015, due to a number of new rental projects that entered the market.

Source: Rentals beware: Market could be heading for a slowdown