Malaysian authorities were on the lookout for boats believed to be carrying up to 200 Rohingyas after dozens of migrants were found near a beach in the country's north yesterday.

Scores of Rohingya Muslims have boarded boats in recent months to try to reach Malaysia, part of what authorities fear could be a new wave of people smuggling by sea after a 2015 crackdown on trafficking.

Forty-one Rohingya men and boys, aged between 14 and 30, were detained yesterday near the town of Simpang Empat after landing at Sungai Belati beach, state police chief Noor Mushar Mohamad said in a statement.

Thirty-five migrants landed at the same beach last month in the northern state of Perlis, bordering Thailand.

More boats carrying about 200 Rohingya migrants are believed to be at sea, Noor Mushar said.

"If we find them in our waters, we will bring them to shore," he said, adding that it was not clear if this group was travelling from Bangladesh or Myanmar.

More than 700,000 Rohingyas crossed into Bangladesh in 2017 fleeing an army crackdown in Myanmar's Rakhine state, according to UN agencies.

Myanmar regards Rohingyas as illegal migrants from the Indian subcontinent and has confined tens of thousands to sprawling camps in Rakhine since violence swept the area in 2012.

The unrest prompted tens of thousands of Rohingyas to flee Myanmar by sea. The exodus peaked in 2015, when an estimated 25,000 people crossed the Andaman Sea for Thailand, Malaysia and Indonesia, many drowning in unsafe and overloaded boats.

The boat that arrived off Perlis yesterday was carrying 47 Rohingyas, all of whom paid a Thai trafficker 4,000 ringgit ($976.80) each to take them to Malaysia, Noor Mushar said, citing interviews with one of the detainees.

The group had been travelling with hundreds of other Rohingyas on a larger boat before they were transferred to smaller, crowded vessels in Thai waters, he said.

The 47 migrants were dropped about one kilometre offshore and walked for an hour through mud. Forty one were detained and six people are missing, Noor Mushar said.

"Since there was no one to greet them, they made their way in separate groups to the nearby villages, covered in mud," he said, adding they were in good health despite their ordeal.