By Trinna Leong

KUALA LANGAT Malaysia (Reuters) - An overloaded boat carrying suspected illegal Indonesian immigrants sank as it left Malaysia's west coast early on Wednesday, and at least three passengers drowned and 34 were missing.

The boat, whose passengers included women and children, sank at the mouth of a river shortly after midnight as it left Malaysia's Carey Island, likely bound for Indonesia's Sumatra island, officials and witnesses said.

Police said the boat lacked safety equipment such as life jackets, but that rescuers were still holding out hope of finding more survivors. The boat went down in shallow water close to shore.

"It is likely that survivors could have swum ashore and went into hiding since they have no legal documents here," said Mohammed Hambali Yaakup, head of operations in the area for the Malaysian Maritime Enforcement Agency (MMEA).

Hambali said he could not confirm reports that a people-smuggling gang had been involved with the boat. All 60 survivors have been arrested under immigration laws, he said.

Malaysia, one of Southeast Asia's wealthier economies, has long been a magnet for illegal immigrants from Indonesia and other poorer countries in the region. Many undocumented Indonesians work in Malaysia's extensive oil palm plantations, a mainstay of its economy.

"This was an illegal boat and all the passengers were Indonesian," Mohamad Zuri, another MMEA official told Reuters.

Police said two bodies had been recovered. A Reuters reporter saw three bodies - two on the deck of a rescue boat and another washed up on shore.

Rescuers were scouring the area for survivors and had deployed a helicopter, one large ship and eight smaller boats in the operation, officials said.

Despite periodic crackdowns on illegal workers, Malaysia is home to an estimated 2 million undocumented immigrants or about 7 percent of its 29 million population.

The question of migrant workers has long been a touchy issue in Indonesia. Both candidates in a July 9 Indonesian presidential race have said that Indonesian workers overseas, often doing menial labour, need better protection.

(Additional reporting by Al-Zaquan Amer Hamazah and Anuradha Raghu; writing by Stuart Grudgings; Editing by Nick Macfie and Robert Birsel)