Last year, several luxury  Vietnam hotels pledged to develop new properties in the country, adding to a hotel surge that began 10 years ago.

The development contributed to a 36% boost in visitors in the first half of 2010, making Vietnam fourth in the world in tourism growth, according to the World Tourism Organization.

Meanwhile, several river cruise operators say that demand for Mekong River trips is pushing them to develop or rapidly expand cruise programs there.

While those sectors have only recently discovered Vietnam, the upscale and expedition sector of the cruise industry was on the forefront of travel to the country, with several first visiting Vietnam in the early 1990s.

Even back then, when its inland tourism infrastructure was lacking, Vietnam’s 2,140-mile coastline made it geographically suited to cruise exploration.

Recent tourism development has benefited the cruise industry, bringing needed infrastructure and excursion opportunities. But the same development also threatens to change much of what visitors find so charming about Vietnam.

“The demand for Vietnam is very high among sophisticated travelers because the destination offers a glimpse into ‘old Asia,’” said Mark Conroy, president of Regent Seven Seas Cruises, which began operating in Vietnam when the country’s ports opened in 1992.

Vietnam is not as developed as many Asian cruise destinations, such as Hong Kong, Singapore and, increasingly, Shanghai and Beijing.

This has traditionally made Vietnam challenging to travel to by land, but it also enabled it to retain a pristine, old-Asia ambience that one well-traveled passenger on a recent Silversea Cruises itinerary likened to “China in the 1970s.”

Silversea has been offering cruises to Vietnam since 1996. It is among several cruise lines that say Vietnam’s overall tourism infrastructure had greatly improved.

Steve Tucker, Silversea’s vice president of field sales, said the country was doing an “excellent job cultivating cruise business.”

“Every year we notice significant improvements,” Tucker said. “When we first started visiting Vietnam, tour buses were of very poor quality and had no air conditioning. Currently, buses are much more modern and significantly more efficient. Roads leading to popular tourist spots are now newly paved and in better condition. Public restrooms are more plentiful and in better condition.”

Tucker also noted that the language skills of Vietnamese guides have greatly improved.

“It’s not uncommon now to find guides speaking multiple languages,” he said. “In the past, we were hard pressed to find even an English-speaking guide. Having guides that are multilingual is extremely important to our international clientele looking for private tour arrangements.”

Another improvement Tucker cited is faster port clearance times and customs procedures, which enable passengers to disembark soon after arriving.

“Years ago, it would take some time before our guests were allowed to go ashore,” he recalled.

Travel agents say cruise ships exposed people to Vietnam, and now they want to go back for land stays.

“Cruises have helped give more awareness to the destination,” said Susan Reder of Frosch Classic Cruise and Travel in California, who herself first visited Vietnam many years ago on a cruise. Today, she said, the destination is “definitely hot.”

“There are so many new properties opening up in Vietnam,” Reder said. “It’s a fabulous country, so interesting; wonderful people and the best food.”

Cruise lines say demand for Vietnam is as strong as ever and, in fact, still growing.

Silversea said interest in Vietnam has grown even as demand for other Asian destinations has diminished.

“Indonesia used to be the hot Asia destination,” Tucker said. “Now it’s Vietnam.”

Adam Snitzer, vice president of marketing for Seabourn Cruises, said Vietnam was one of the line’s most popular destinations not only in Asia but worldwide. He also noted that Seabourn cruises go to Vietnamese destinations that can be “challenging if done by land.”

Seabourn, which has been calling in Vietnam since the early 1990s, recently added Sihanoukville in Cambodia to the line’s 2012 Vietnam/Thailand cruises in order to offer access to Angkor in Cambodia, Snitzer said, noting that its passengers “do seek new and more exotic destinations.”

Despite continuing developments, the lines also cite some challenges there.

Conroy noted there were “some bureaucratic issues with the government” that passengers rarely see. He added that Regent’s main challenge can be getting people to Vietnam.

“The biggest challenge in the area are the distances and the cost to get there,” Conroy said, noting that with flight time up to 24 hours, many people want to travel in business class, which, depending on capacity and demand, “can be expensive.”

He also said that unlike in Europe, Regent can’t depend on the local market to fill a portion of the ship.

“In Asia, for luxury we have not seen the demand,” Conroy said, adding that Regent’s Asian guests mostly travel in Europe or Alaska.