A horrific motorcycle accident in Thailand on New Year's Eve claimed the lives of two Singaporeans.

Miss Vanalyn Png, 22, had been in intensive care at a local hospital with broken arms and internal bleeding in her head and abdomen, according to her brother Jervis. She died just past midnight yesterday.

"The doctor tried hard, but they couldn't save her. Vanalyn fought the battle bravely and she lost... She's now in a better place," Mr Png said in a Facebook post.

Miss Png was a pillion rider on the motorbike ridden by fellow Singaporean Ng Yong Sing, 27.

Mr Ng died when the pair were thrown into a 3m-deep drain in southern Phatthalung province, according to reports.

A local rescue group, Rescue Phatthalung, said the accident occurred at 1.20pm on Sunday.

The Singapore-registered motorcycle is believed to have skidded on the wet road.

Mr Png, 24, and his other sister Vanessa, 25, told The Straits Times at their Woodlands flat that their younger sister was a vocal and affable person who enjoyed sports, once helming the Singapore Polytechnic marathon team and leading her secondary school's basketball team as its captain.

Both Mr Ng and Miss Png were employees at the Select Group food and beverage conglomerate, they added.

Mr Ng was a business development executive who recently received a scholarship from the company, while Miss Png started at the firm as a marketer less than six months ago.

The pair left for Malaysia on Saturday and were due to return to Singapore today.

But Miss Png's siblings said their sister had not told the family that she was heading to Thailand, though they knew she would be in Malaysia. They were also not told that she was travelling with Mr Ng or doing so on a motorcycle.

"If she had told us, we would have discouraged her from riding a motorcycle there. We were under the impression that she was taking a bus with friends," said Mr Png, describing his sister as an independent spirit.

The motorcycle, a Honda CB400 Super Four, is believed to have belonged to Mr Ng.

Mr Ng, whom the Pngs described as outgoing and just as talkative as their sister, had visited their family three times in the past year on a similar motorcycle.

Both victims' parents are heading to Thailand to retrieve the bodies, said Mr Png.

The Straits Times understands that the Singapore Embassy in Bangkok is helping both families.

This was the fourth reported case in December of a fatal traffic incident involving Singaporeans in a foreign country.

On Dec 22, a car crash in the United States killed 22-year-old Singapore Armed Forces scholarship holder Justin Yeo Jun Xi and his parents. His 19-year-old sister Justlyn Yeo Jing Hui survived.

A day earlier, interior designer Koh Yuan Ling died in an accident while travelling in South Africa with her sister, who has since been discharged from hospital.

On Dec 11, Mr Seow Kai Yuan was killed in an accident in New Zealand's State Highway 6 on the west coast of the South Island.