The two Singaporeans reported missing while kayaking off Mersing, Johor, are likely proficient in the sport.

Mr Tan Eng Soon, 62, and Madam Puah Geok Tin, 57, most likely attained four-to five-star certification, which signals that they are competent enough to kayak in the open sea.

The two were reported missing on Friday, after they drifted apart from a group of around 13 other Singaporeans that they were kayaking with.

Singapore Canoe Federation's online resources showed that the "4 Star Award - Sea" certification confirms one's "competence to journey on technically demanding water requiring judgment and refinement of basic strokes, skills and techniques".

Environments requiring this minimum certification would include sea and open water with waves of half a metre in height.

To receive the four-star award, enthusiasts would have to commit to four full days of training.

They would also have to attend 10 open-water journeys of 16km each on at least two different sections of Singapore's coastline.

A five-star award would certify candidates to venture into more advanced levels of kayaking, where they might encounter waves of at least 1m in height.

They have to be extremely proficient at kayaking, and must have made at least five sea journeys of 30km each, among other criteria.

The pair were in turbulent waters with strong winds when they went missing. Enthusiasts here said that paddling a significant distance in such conditions would have been difficult even for young sportsmen.

Wind speeds in the area where they went missing can go up to 40 and 50kmh.

"The one thing that is dangerous about kayaking in the open sea is sudden shifts in the weather that might cause the winds to pick up and waves to get volatile and sometimes deadly," said Mr Desmond Lim, 49, who has been kayaking for 18 years.

People who want to kayak long distances, regardless of age, are advised to pack basic first-aid supplies, as well as food and bottled water in a waterproof backpack, just in case things go awry, Mr Lim said.

"I would definitely advise all who intend to go kayaking out in the open sea to ensure that their life jackets are functioning properly, and pack some emergency supplies in waterproof bags, including a small flashlight and a compass," he said.

The group had seized the opportunity to go kayaking off Mersing over the long weekend. Madam Puah and Mr Tan are believed to have been last seen on the same bright green kayak.

Shin Min Daily News reported Madam Puah's husband - 59-year-old retiree Pang Wenjie - as saying that his wife and Mr Tan did not know each other before the trip.

The families of both missing kayakers are in Malaysia.