Two fire technicians working at a US research station in Antarctica have died after being found unconscious.

The men were found on the floor of a building which houses a generator for a nearby radio transmitter, after a helicopter pilot flying over the area saw what appeared to be smoke coming from it and landed to investigate.

One of the technicians was pronounced dead at the scene and another died a short time after being flown to the McMurdo medical clinic, which is managed by the National Science Foundation (NSF). The NSF said the incident is under investigation.

The men had been working on a fire-suppression system at McMurdo station on Ross Island when they were discovered.

The research station, established by the United States in 1955, is situated near Antarctica’s McMurdo Sound, named for a British naval officer who was part of the expedition that first charted the area in 1841.

The largest outpost in Antarctica, it lies at the tip of Ross Island in the New Zealand-claimed territory known as the Ross Dependency. The incident happened on December 12 local time, which goes by New Zealand time.

Daytime highs in December, in the middle of the Antarctic summer, average 31.5 degrees Fahrenheit or -3 degrees Celsius. More than 1,000 people, including scientists and support personnel, work at the station this time of year.