The Malaysian authorities ramped up their search efforts for the two Singaporean kayakers yesterday, as their relatives refused to give up hope - with one likening her missing aunt to adventurer Bear Grylls.

Madam Puah Geok Tin, 57, and Mr Tan Eng Soon, 62, were kayaking with a group when the pair's bright green double kayak went missing last Thursday.

Yesterday, Madam Puah's niece, Ms Jen Pan, who was with other family members at Penyabong jetty waiting for news of the kayakers, said: "My aunt is not your typical auntie. She's like a female version of Bear Grylls."

Ms Pan, 35, said her aunt is "very fit" and heavily involved in different sports, such as cycling, rock climbing and dragon boating.

She added: "She's super strong, physically and mentally... She can survive this."

The Malaysian authorities said yesterday that they had deployed more aircraft and almost doubled the size of the search area, with the region covered by air assets expanding to 900 square nautical miles between the east and north of Pulau Tioman in Pahang.

The area is about 3,000 sq km, or four times the size of Singapore.

The search and rescue (SAR) operation on Sunday had covered 500 square nautical miles in the same area and involved only one aircraft.

Yesterday's search efforts at sea, on the other hand, encompassed 600 square nautical miles from east of Rompin on Peninsular Malaysia to the north of Tioman.

At a press conference held at Penyabong jetty in Mersing, Johor, the Malaysian Maritime Enforcement Agency (MMEA) said four helicopters, one aeroplane, two ships - including one from the Royal Malaysian Navy - and five boats were deployed yesterday. The operation was conducted from 7.30am to 7pm amid intermittent rain.

The MMEA said it had also sent out a broadcast to fishermen and commercial vessels out at sea to look out for the missing kayakers.

Four multi-purpose vehicles were also deployed to patrol the coastline between Kuala Rompin and Mersing to search for the kayakers, who might have drifted to waters in that region based on wind directions. A total of 104 men were involved in yesterday's search.

First Admiral (Maritime) Aminuddin Abdul Rashid, director of Johor MMEA, said Malaysia has the full ability to conduct SAR within its own waters and does not need assistance from neighbouring countries.

The Malaysian authorities had said earlier that erratic weather due to the monsoon winds was hampering the SAR team.

Madam Puah and Mr Tan were separated from their group in the Endau waters in Mersing last Thursday evening, after experiencing strong winds and choppy waters.

A police report was made the next day and an SAR team was sent out at around 3.30pm the same day.

Four members of the group have stayed on in Mersing while the rest have returned to Singapore.

The four are close friends of Madam Puah, who is a businesswoman, and have known her for over 30 years. Madam Puah's husband, Mr Peng Mun Kit, 56, said: "My wife was like a sister to them."

The friends said they were paddling at the front of the group last Thursday.

One of them, who wanted to be known only as Mr Tay, said they realised one kayak was missing only after they went ashore on Pulau Mertang Timur, the island that was the intended destination for that leg of the expedition.

Another of the four friends, who is also Madam Puah's godsister and wanted to be known only as Madam Ong, said: "Given the situation at that time, even if you had blown a whistle, you wouldn't be able to hear it (over the choppy waters).

"All of us just followed (the leader). We trusted the organiser."

The five-day expedition was organised by Mr Goh Khee Wei, who was also the guide for the group.

After the group discovered that Madam Puah and Mr Tan's kayak was missing at around 6pm last Thursday, Mr Goh called for a speedboat to search for them. They gave up at around 8pm after it became too dark.

The group rested overnight on the island. At 7am the next day, Mr Goh went out with the boatman on the speedboat to the mainland to get help and make a police report.

The Straits Times understands Mr Goh was born in Malaysia and is a Singapore permanent resident.

The other team members said they did not know Mr Goh personally before joining the expedition but heard that he had organised many similar kayaking trips before.

ST understands that Mr Goh manages a group called Kayak Kakis on the Meetup app, which some members of the expedition are a part of.

Mr Goh was one of four people in the expedition who had kayaked the same route as the one in the expedition, while the other members have gone on different journeys around Singapore, such as at the Southern Islands.

Most of them are understood to have had some form of experience in dragon boating or canoeing.

The group had trained on weekends two months prior to the trip by going on weekly sea expeditions around Singapore, such as around Pulau Ubin and around the waters in Sembawang.

According to Mr Tay, the youngest member of the group is 39 while the oldest is believed to be the missing Mr Tan, who is 62. He is believed to be a retired lawyer.

Mr Tay, 56, said he was unaware that they had to get a permit from the Malaysian maritime police in order to go on a sea expedition in Malaysian waters.

"We were too naive," said Mr Tay, adding that they joined the trip at the invitation of friends without finding out much about what to do.

An MMEA spokesman said: "(For) any activity in the sea, especially those involving groups, you need to get approval from the Malaysian Maritime Enforcement Agency and the Royal Malaysia Police."

Mr Tay said: "I hope this incident will remind Singaporeans to do things like getting a permit (from the MMEA) and informing the MFA (Singapore's Ministry of Foreign Affairs) before going on trips like that."

As of press time, there were no further updates regarding the missing pair. Earlier, MMEA zone commander of Mersing Haris Fadzillah Abdullah said searches typically last no more than seven days but can be extended if the need arises.

He could not confirm whether the Malaysian authorities would increase manpower and assets today if no progress had been made.

• Additional reporting by Trinna Leong