United States carrier Delta Air Lines will be leaving the Singapore market by the end of next month, amid increasing competition on US routes from airlines such as Singapore Airlines (SIA).

The airline said in a statement on Saturday (Aug 3) it will suspend its Singapore-Narita service from September 22. It added that its customers can continue to fly to Singapore via Seoul, through Delta’s partnership with Korean Air.

Changi Airport Group (CAG) said yesterday affected passengers are advised to contact the airline for other options.

A CAG spokesman said Singapore residents will continue to be well served on US routes, despite Delta's exit. He added that there are 71 weekly services to five cities, including 45 non-stop.

"We will continue to keep in touch with Delta and look forward to welcoming the airline back to Changi Airport in the future."

Other airlines at Changi Airport currently offer flights from Singapore to Houston, Los Angeles, New York/Newark, and San Francisco in the US.

From Sept 3, SIA will offer non-stop flights to Seattle.

Mr Brendan Sobie, chief analyst at the Capa Centre for Aviation, told The Straits Times that the writing had been on the wall for Delta for some time.

"SIA and United have been more aggressive as they have launched non-stop US flights.

"Non-stops are the future for the US market here, and Delta has been very conservative and has lost out. Delta is very small here and their market has declined as competitors expanded," he said.

Citing the example of SIA's upcoming direct flight to Seattle, Mr Sobie said Delta had looked at the possibility of offering one as well, but decided against it.

Delta then lost its opportunity to do so after SIA announced in November last year that it would launch the route.

SIA currently holds the record for operating the world's longest commercial flight with its Singapore-Newark service.

Analysts said SIA made a sound business move in reinstating non-stop services to the US.

It had previously axed direct services to Los Angeles and New York in 2013 due to high fuel prices and weak demand.

Experts have also said that travellers are choosing non-stop flights for reasons such as saving travel time.

Travellers typically expect to pay more for non-stop flights than for flights with stops, but checks show that there is often little difference between the two.

Mr Tan Aik Hui, 22, who studies in Tokyo, said he will miss Delta's airline deals for Japan.

He had booked a round trip to Singapore for about $700 and is due to fly back on Sept 22, which could be the last day of Delta's operations here.

"It was about $65 cheaper than the next cheapest option... I did expect to use it more in the future," he said.

"I am lucky that I managed to grab it this time round, but not so lucky that it has been discontinued."