Dozens of Rohingya are believed to have died during a four-month boat journey to Malaysia, a coastguard official said on Wednesday.
There had been more than 300 people on board the boat which was intercepted by authorities earlier this month, said Datuk Mohd Zubil Mat Som, director-general of the Malaysian Maritime Enforcement Agency.
The 269 survivors were taken to Langkawi.
"Some of them died at sea. They were thrown overboard," Zubil told reporters, without specifiying the exact number.
Zubil said the group had been on a "motherboat" carrying more than 800 people before being transferred to a second vessel.
Authorities have not found the original boat thought to be now carrying around 500 people.
"We cannot locate them," he said.
Malaysia is a favoured destination for Muslim Rohingya fleeing violence in mostly Buddhist Myanmar, with thousands trying a perilous escape via smugglers across the sea every year.
Rohingya usually travel either from Myanmar or Bangladesh, where about one million live in squalid refugee camps. Most of those fled a 2017 military crackdown in Myanmar.