Fashion designer Jason Wu lovingly refers to a handbag, the Daphne, as one of his label's "classic bags." The bag isn't from decades or even years ago: It made its debut in stores last year. This "classic" represents the new, faster cycle of designer goods.

Mr. Wu, along with other young designer labels, are quickly adding collections of bags and shoes, launching secondary lines or small collections for other brands. Some are opening their own stores and expanding abroad much earlier than their predecessors did. In the process, they are upending fashion's playbook.

The voracious appetite for newness from retailers, fashion magazines and the fashion blogosphere is also pushing younger designer labels to grow up much faster than labels that launched in the 1980s and '90s. Unlike other industries, it isn't production breakthroughs spurring the pace of product launches. Instead, the change is more about the style sector's lightning-speed buzz factor: Today's wannabe is tomorrow's in-demand designer who is increasingly striking with new lines while the iron is hot.

By moving quickly, young labels also risk overexposure, diluting their reputations and, by having their hands in too many things too soon, sacrificing quality. Expanding into accessories and other categories also generally requires investment in staff and production, putting additional financial strain on these young often fledgling labels. The alternative is to sign up with a licensing partner and hope the product will be consistent with the designer's aesthetic and standards.

This faster pace will be on display at New York Fashion Week, which starts Thursday. Accessories have proven lucrative growth engines for the luxury-goods industry. While it has become customary for established designer labels with long careers to present accessories during this week, more recent fashion labels like those of Mr. Wu and Alexander Wang—who launched bags in 2008, just one year after debuting his women's collection—are cranking out accessories and splashily sending them down the runway.

Mr. Wu, 29-years-old, plans to debut a new line of bags on the runway Friday. He is known for a polished, ladylike style and presented his first ready-to wear-collection in 2006. Just two years later he launched a Resort collection in addition to Spring and Fall lines. His breakthrough moment arrived in January 2009, when first lady Michelle Obama wore a custom-made, ivory silk-chiffon Jason Wu gown to the inaugural balls. A flurry of activity followed, including an eyewear collection with Modo in fall 2009, two capsule collections—a sort of mini collaboration—for clothing line TSE, a nail-polish collaboration with CND and a cosmetics collaboration with Supreme Aupres in 2010. Mr. Wu's handbags and shoes debuted in stores in 2011. This year, he made a candle with Nest fragrances, as well as a collection of clothes, handbags and scarves for Target. His secondary line, Miss Wu, is set to arrive exclusively at Nordstrom stores in January. All the while, he produces four Jason Wu ready-to-wear collections a year.

"You can't just follow the path of designers before," Mr. Wu says of his generation of designers. "It was a different world then."

Marchesa, a label known for lush and intricate evening gowns, launched a diffusion, or secondary, line called Notte by Marchesa in 2006, two years after launching its main line. It has since launched a handbag line, wedding dresses, a tabletop collection with Lenox, and a limited-edition cosmetics collection with Le Métier de Beauté. The brand plans to launch a fragrance this week. A "contemporary line" featuring more daywear is set to debut in 2013.

Phillip Lim opened a New York store a little more than a year after debuting his women's line, 3.1 Phillip Lim, in 2005. Two stores, in Tokyo and Los Angeles, followed in 2008. The label then opened stores in Seoul, Singapore and Hong Kong. The stores were partly a way for Phillip Lim to control the way he wanted his line to be presented.

"I'm not sure if we were supposed to do that or not," says Wen Zhou, chief executive of Phillip Lim, referring to the opening of a store so soon after launching. "We just said, 'we can do that.' We didn't look at other brands, at how they opened stores," she says. "It might seem fast or quick but it felt right at the time. We don't follow any playbook." The label launched bags and shoes early last year.

By contrast Narciso Rodriguez, in business with his own line since 1997, just launched shoes and bags earlier this year.Marc Jacobs, who launched his women's collection in 1986, opened his first store in 1997 and started selling a diffusion line, Marc by Marc Jacobs, in 2001. Donna Karan launched her separate DKNY line in 1989, four years after the debut of her main collection. She opened her first DKNY store in 1994 and her Donna Karan Collection store in 1996. (Donna Karan offered accessories from the beginning.)

To be sure, each fashion house has different reasons for the timing of, say, an accessories line or a store. Still, these days, it is the rare designer label that can afford to ignore accessories or other brand extensions.

"If you look at 15 years ago, you did your main line, after five years you do an accessories line, you could end up doing a secondary line and save the fragrances and sunglasses for the end of expansion," says Robert Burke, a luxury-goods consultant and a former fashion director at Bergdorf Goodman. "Today those rules don't apply," adds Mr. Burke, who has advised young labels including Mr. Wu's.

"People like Ralph Lauren and Giorgio Armani took a generation to develop their reputation in apparel before starting accessories. Now if somebody is hot very quickly, they want to exploit it pretty quick," says Arnold Aronson, managing director, retail strategies at consulting firm Kurt Salmon. "You can do it but you have to say to yourself is my career as a designer going to be a marathon or a 50-yard dash?"

Both Target and Nordstrom approached Mr. Wu about doing less-expensive lines a couple of years ago, but he declined, thinking the timing wasn't right, he says.

He eventually launched a line with Target, in February, which "showed me that there was really an appetite for my design," at lower prices, and making him reconsider the Nordstrom offer, he says.

"There are some things that I cannot or will not make for my collection because it would not be the right price point, like a T-shirt. [But] there was a price point I was not reaching," says Mr. Wu of the Nordstrom deal. Jason Wu's dresses average $1,595 while Miss Wu will reportedly range from about $200 to $800.

U.S. sales of women's bags and luggage rose 6% to $9.92 billion in the 12 months ended July 31, according to market researcher NPD. That compared with a 4% rise to about $108.28 billion for women's apparel. Sales of women's fashion shoes rose nearly 3% to $17.45 billion.

Mr. Wu says launching bags and shoes last year "allowed us to reach out to a broader audience that knows Jason Wu" but may not be able to comfortably afford his ready-to-wear clothes, where prices range from $595 for knitwear to $6,360 for an evening gown. By contrast, Jason Wu bags range in price from about $1,500 to about $3,000. Shoes cost $630 to $1,470.

Gustavo Rangel, Jason Wu's chief financial officer, says the label's shoes and bags already represented 17% of the closely held company's sales last year. He expects them to represent 25% of sales this year and 40% in the next few years.

Mr. Wu conceded that as a clothing designer, he lacked the skills to produce accessories. "I had to learn from the ground up," he says. He has since hired a two-person design team for accessories. The eyewear collection is licensed out.

Mr. Wu says he can appreciate some observers may feel he's juggling too many balls. "It's only too much when there's no market for what I do," he says. "If there's a legitimate market for Jason Wu, why not?"