The rescue workers were swept away by fast currents when the boat they were travelling in overturned in Kedah state, the official Bernama news agency said.

"Search and rescue operations for the four are ongoing, their fate is unknown," said a spokesman for the district floods operation centre, adding that the workers were patrolling affected areas when the accident happened.

Police said the confirmed fatalities were a disabled 22-year-old girl who drowned in Terengganu state and a five-year-old boy thought to have drowned in a canal in Kelantan on Sunday. His body was found in a rice field some distance away from his father's car, where he had been left several hours earlier.

Flooding has hit five states -- Perlis and Kedah in the north, Kelantan and Terengganu in the northeast and north-central Perak.

Some 11,000 people have been evacuated from Kedah, while 4,500 residents in Perlis, 5,475 in Terengganu, 2,713 in Kelantan and about 100 in Perak have been shifted to relief centres, according to local police and Bernama.

But particularly in the northeastern states where the situation has eased, several thousand are believed to have returned home already.

Deputy Prime Minister Najib Razak was scheduled to arrive in the affected areas later Monday.

The meteorological services department issued a tropical storm warning on Sunday after detecting a depression over the South China Sea, and said strong winds and rough seas were expected to persist until Tuesday.

Train services connecting the north to Thailand were disrupted by the floodwaters, which rose to 10 feet (three metres) above the track in some areas.

Workers were waiting for levels to drop before repairing a damaged stretch of the line between Kuala Lumpur and Hat Yai in southern Thailand, said Azizah Ujang from national rail company KTMB.

International service linking Bangkok and Malaysia's northern Penang state was terminating at a Malaysian border town instead of continuing on to the state's capital, Butterworth, the spokeswoman said.

"It is very difficult for us to clear the tracks. The water has not subsided yet," she told AFP, adding that the firm hoped to clear the route by Monday evening.

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