Retail rents are firming up, having started off with a great autumn that lifted six of Manhattan’s 17 prime shopping corridors into positive territory with one flat versus four positive — compared with one flat just a year ago, The Post can exclusively report.

The largest jumps were in the corridors populated by both locals and tourists with limited inventory, according to the new Real Estate Board of New York spring retail report.

Deals in the first few months of 2019 were driven by the food and beverage industry, followed by activewear, cosmetic and technology brands, the report states.

Downtown had the largest upswing as lower Broadway rents have leaped 19% since the fall, to $401 per square foot. In Herald Square and the rest of the area along West 34th Street, rents since the fall were up 7%, to $613 per square foot. In Times Square, rents turned from flat to fluff, rising 4%, to $1,936 per square foot — with a range of $1,500 to $2,350 per square foot — amid stronger demand and lower-priced spaces coming off the market.

Up 2 percent since last fall are Billionaires’ Row on East 57th Street between Fifth and Park avenues, Fifth Avenue in the Flatiron District between 14th and 23rd streets, and Fifth Avenue’s luxury stretch from 49th to 59th streets. The latter “high street” area is maintaining the top asking rents in the city, ranging from $2,000 to $4,000 per square foot as several large availabilities remain vacant — but is still down 22% since a year ago.

Even as dealmaking is up along Madison Avenue from 57th to 72nd streets, as those higher up on the avenue seek better-located spaces, rents fell another 10%, to $1,039 per square foot, and are down 25% since last spring.

Broadway between 72nd and 86th streets also fared poorly as rents fell 11%, to $273 per square foot, and down 16% from one year ago, with Columbus Avenue down 6%, to $279 per square foot since fall, as the city’s rules banning larger storefronts continue to stymie retailers.

Harlem’s 125th Street and Broadway in both the Flatiron and in Soho were all down 2%. The latter is also struggling as pop-ups persist and longer-term luxe tenants remain on side streets. T.J.Maxx’s opening at 473 Broadway between Broome & Grand may prompt other off-price chains to dig in.

Brokers and owners are revving up for next week’s International Council of Shopping Centers confab in Las Vegas, where new availabilities are expected to be revealed, including Vornado’s Farley train station plans.

Inventory also increased as owners reinvented buildings and high-profile projects came on line, including Hudson Yards, Gansevoort Row, the Seaport District and Essex Crossing.

Local brokers, however, have also brought forth their most creative and important deals from 2018 and are now vying for REBNY’s annual Retail Deal of the Year competition.

Downtown is dominating the nominations with just one of the five deals completed uptown.

The uptown nomination — a 17,530-square-foot lease that brought Ikea’s urban strategy of “delivery only” to 999 Third Ave. across from Bloomingdale’s — was completed by the Colliers International team of Eric Yarbro, Robert L. Freedman, Jonathan Plotkin, Taylor Bell and Timothy Pond.

Noho is the beneficiary of Showfields, a clicks-to-consumer department store that opened in 14,707 square feet on all four stories of 11 Bond St. on the southwest corner of Lafayette Street. Brandon Singer of Cushman & Wakefield represented this concept, which includes a rotating cast of fashion concepts that sublease their spots along with two stories of rotating art and another with co-working and event space. A 1,700-square-foot roof terrace boasts 1,500 square feet of covered support areas. Christopher Owles of Sinvin Real Estate advised the RFR ownership.

In Hudson Square, Robin Abrams, Lisa Rosenthal and Curtis Woodside of the Abrams Retail Strategies at Compass brought the San Francisco pop-up Color Factory for a two-year lease of 11,000 square feet at 150 Varick St., aka 251 Spring St. The experiential art exhibition has become a must-see attraction that celebrates color in 16 rooms with 20 “color experiences” designed by artists and set up for hands-free selfies.

In the Financial District, Life Time fitness leased 72,260 square feet in mostly underground space in the base of Harry Macklowe’s reimagined luxury residential project at One Wall St. An RKF team of Peter Whitenack, Jackie Totolo and Scott Zinovoy represented the building while the Dartmouth Company’s Joe Mastromonaco and Fritz Kemerling worked out for the fitness company.

Nearby, a lease of 40,000 square feet with Alamo Draft House at 28 Liberty St. kicked off the leasing and amenity-friendly renovation of the plaza at the base of the former One Chase Manhattan office building.

Newmark Knight Frank’s Jeffrey D. Roseman and Ross Kaplan represented the Fosun ownership.

The awards for the most ingenious and significant deals will be announced at the 21st Annual Retail Deal of the Year Awards Cocktail Party on Tuesday, June 11, at Convene’s 117 W. 46th St. location.