The running had to be done in soft snow and in temperatures as low as about minus 35 deg C, after considering wind chill. Then, there was the threat of polar bears attacking.

But all three Singaporeans who took part in the North Pole Marathon successfully finished the run on Sunday.

Ms Gloria Lau, 64, who covered only 28km in last year's race, ran the full 42.195km distance this year and finished in 11hr 29min 45sec.

This makes her the first Singaporean woman to finish the full North Pole Marathon.

Mr Ong Tze Boon, 47, group executive chairman at environmental design solutions firm Ong & Ong and son of the late president Ong Teng Cheong, finished the race in 6hr 39min 48sec.

His cousin Ong Yu-Phing, 46, an IT director at Ong & Ong, finished in 9hr 4min 25sec, according to provisional results on the event's Facebook page.

The race was scheduled to start on April 9, but was postponed by about a week as cracks formed on the runway. This made it unsafe for planes carrying the runners to land on the ice sheet in the Arctic Ocean.

The Singaporeans - among the first group of runners to fly in from Svalbard, Norway - arrived at the North Pole camp last Thursday.

But that day, event organisers wrote on its Facebook page: "Significant cross winds caused a crack to develop in the runway and, with the second plane-load of competitors just 15 minutes from landing, they were ordered back to Norway."

So, the race started at 2pm GMT last Saturday instead, after all 47 runners had arrived.

All the Singaporean participants ran for charity. Ms Lau, who runs a property development business, said people can tell her which charity they want to donate to, and she will match the amount dollar for dollar. The Ong cousins hope to raise funds for five charities that support mental health, including the Singapore Association for Mental Health.

Mr Ong Yu-Phing told The Straits Times: "I'm elated to have finished the race and honoured our fund-raising campaign."

He added: "The numerous delays are part and parcel of the race. It is definitely not for the faint-hearted."

•To support the runners' fund-raising efforts, e-mail Ms Lau at gloria235id@yahoo.com, or go to runwithyourheart.ongfoundation.org