Hell's Kitchen, is now being associated with another nickname: Thai Town.

For more than a century, the midtown neighborhood west of Eighth Avenue has been known as Hell's Kitchen. Now, another nickname for the area is emerging: Thai Town—a nod to the growing number of Thai restaurants cropping up along Ninth Avenue from West 34th to West 57th streets.

Restaurateurs in the area estimate that there are some 40 Thai eateries, mostly small and budget friendly with quirky names including Tai & Thai, Tiny Thai Café and Pam Real Thai Food.

Though Ninth Avenue has long been known as a destination for inexpensive ethnic restaurants, Thai eatery openings have accelerated in the past four years, according to Darrick Sampson, past president of the West 46th Street Block Association.

The trend began with Nirun Jetanamest, a Thai immigrant who opened Yum Yum Bangkok on Ninth Avenue between West 45th and West 46th streets in 1998. He now owns four restaurants—including three named Yum Yum—all within a block of each other. Some consider him Thai Town's unofficial mayor.

“Everyone knows Nirun. He is a big person in the Thai community,” says Suraschai Plaibua, general manager of Room Service, a chic restaurant that moved into the neighborhood in March.

The restaurant business can be highly competitive, but the Thai countrymen seem indifferent to such pressures. While Mr. Plaibua's Room Service was under construction earlier this year, Mr. Jetanamest invited him and the owners to dine for free at his restaurants.

“He welcomed us to Ninth Avenue,” says Mr. Plaibua.

Mr. Jetanamest earned attention last year by making a bold move—he opened Yum Yum Too on West 46th Street and Ninth Avenue, directly across from his Yum Yum Thai and Vietnamese. He figured customers would consider the proximity a sign of success.

“When people see we have the same name, they will think the food should be good because you wouldn't have two the same that were bad,” he says. It also helped that the building's landlord, a fan of his restaurants, offered him the space.

A lifetime in the food business

At age 70, Mr. Jetanamest has a lifetime of experience in the industry. He immigrated to New York in 1974 to better support his family, who stayed in Thailand. Earning meager wages as a cook and waiter, including at the Waldorf Astoria, he still managed to scrape together $30,000 with his roommate to open his first restaurant in 1991. Little Bangkok on West 54th Street closed four years ago, when the landlord sold the building.

His daughter, Narisara, describes him as a visionary.

“I remember there were drug dealers and prostitutes along Ninth Avenue when we first opened Yum Yum,” she says. “I didn't think we would be busy, but we had long lines.”

A graduate of New York University's school of hotel management, Ms. Jetanamest, 34, helps run the four restaurants with her older brother, Nares. Their holdings include Bangkok House on Restaurant Row, which they co-own with a cousin.

The family was not always so close-knit. The siblings got to know their father for the first time as teenagers when they arrived in this country with their mother. None of them spoke English, and Mr. Jetanamest still struggles with the language. “My father was like a stranger to me,” recalls his daughter. “But now he is more like a good friend.”

The patriarch says he wants to retire to Thailand, leaving the business to his children, but his daughter doesn't believe he can stop working. Mr. Jetanamest isn't sure, either, as he muses about opening a fifth Yum Yum in Pennsylvania, where the rents are much lower.

In the meantime, the current group of restaurants is weathering the economic downturn well. Recession-friendly prices such as $7 for lunch specials and $15.95 for a prix-fixe dinner help keep the places full, along with a steady stream of pedestrians from the nearby offices, new residential buildings and theaters. The restaurants earn as much as $300,000 each in annual revenues.

Thai Town has its detractors. Local residents grumble about the abundance of restaurants in the neighborhood and the dearth of other types of retailers, and local landlords are growing wary of the proliferation of Thai restaurants, according to Aaron Gavios, executive vice president of Square Foot Realty. “When there are five in one block,” says Mr. Gavios, “landlords ask themselves whether the block needs another one.”