By Agence France-Presse
The bodies of six women and three men were washed ashore at a beach near the town of Mersing earlier Monday, the Malaysian Maritime Enforcement Agency said.
"We believe there were about 40 Indonesians on the boat and we believe they were illegal immigrants," an agency spokesman said.
The boat was headed from Indonesia to Malaysia when it capsized. A search is underway for the remaining passengers.
No further details were provided but such capsizes are common.
Last November a speedboat believed to be carrying illegal Indonesian migrant workers returning from Malaysia sank near Batam Island, south of Singapore. More than 40 people were missing.