New York’s rental market isn’t cooling down with the weather.

Manhattan’s average monthly rent hit a new record of $6,865 in September, while Brooklyn logged its strongest September leasing activity since 2020, according to Corcoran’s latest rental reports.

The median rent in Manhattan also reached an all-time high of $5,395 — up 2% from August and 9% from a year earlier — as available apartments dwindled.

The borough had 5,015 active rental listings, down 16% annually and the fewest for any September since 2019. Inventory has now declined year-over-year for two straight years.

“Manhattan’s rental market remains defined by a lack of available apartments,” Gary Malin, chief operating officer of the Corcoran Group, said in a statement.

“With demand continuing to outpace supply, competition remains frustratingly intense across much of the borough.”

Larger apartments saw some of the steepest increases. Average rents for two- and three-bedroom units posted double-digit annual gains, with two-bedrooms reaching a record of nearly $8,500 a month.

Even one-bedrooms, which recorded the smallest annual increase at 6%, averaged $5,436 — just $50 below their July peak.

Manhattan’s vacancy rate stood at 1.54%, marking a fifth consecutive month around 1.5% — the longest stretch at that level in nearly six years.

But the squeeze isn’t translating into more signed leases. Manhattan recorded 3,841 new leases in September, down 19% from August and 5% from a year earlier. Corcoran attributed the slowdown to scarce inventory and record rents discouraging tenants from moving.

Apartments also took longer to find tenants, averaging 48 days on the market, up 12% annually, as renters spent more time weighing their options.

Across the East River, Brooklyn’s rental market bucked the usual seasonal slowdown.

The borough recorded 1,407 signed leases, up 10% annually and 3% from August. Since Corcoran began tracking the market in 2019, September leasing had fallen from August every year, by an average of 24%.

Two-bedrooms drove the increase, with 434 leases signed — up 21% from a year earlier. Studio signings were essentially flat at 248, but still marked the strongest September on record for that apartment type.

Brooklyn’s median rent eased to $4,300 from August’s record $4,368, though it remained 5% above its year-earlier level. Average rent rose 3% annually to $4,946.

The modest monthly dip came alongside a sharp decline in available apartments. Brooklyn had 3,428 active listings, down 25% from a year earlier and 11% from August, marking its lowest September inventory since 2022.

“These conditions continue to prop up pricing and create urgency among renters who are searching for new homes throughout the borough,” Malin said.

Brooklyn one-bedrooms averaged $4,218 a month, while studios cost $3,521 and two-bedrooms reached $5,708. Three-bedrooms were the only category cheaper than a year earlier, slipping 1% to $6,885.

Despite stronger leasing activity, Brooklyn apartments spent an average of 53 days on the market — 13 days longer than a year earlier — reflecting more listings that lingered before securing tenants.