More than 2,000 people, including many children, have fallen ill after toxic waste was dumped in a Malaysian river and emitted hazardous fumes over a wide area, an official said Friday.

About 200 schools and nurseries have been closed in the affected area in southern Johor state after a lorry dumped the waste last week. People who inhaled the fumes suffered from nausea and vomiting, and a handful were left in critical condition.

The number of those needing medical treatment has been slowly rising since the crisis began and on Friday the figure stood at 2,355, including 113 still in hospital, local lawmaker Sahruddin Jamal told AFP.

No one has died.

Prime Minister Mahathir Mohamad visited victims in hospital on Thursday and praised the response of emergency workers.

"They have done their job well even though such a case has never occurred (here)," he said, according to official news agency Bernama.

The military has been deployed along with hazardous waste experts, wearing protective suits and masks, to respond to the emergency and clean up the river near the industrial town of Pasir Gudang.

Local media have reported the waste was a type of oil commonly used to lubricate ship's engines which emitted methane and benzene fumes. Up to 40 tonnes of the toxic substance is believed to have been tipped into the river.

Three men have been arrested over the dumping of the waste and face up to five years in jail if convicted of breaking environmental protection laws.

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© 2019 AFP