Kuala Lumpur, Mar 14 (AFP) Over 100 schools in Malaysia have been closed after the dumping of toxic waste into a river caused hundreds of people to fall ill, including many children, authorities said.

A lorry is believed to have dumped the waste in southern Johor state last week, sending hazardous fumes across a wide area and causing those affected to display symptoms of poisoning such as nausea and vomiting.

Over 500 people, many of them school pupils, have received medical treatment after inhaling the fumes, with over 160 admitted to hospital, according to official news agency Bernama.

It was unclear what type of poisonous gas had been emitted near the industrial town of Pasir Gudang.

Education Minister Maszlee Malik initially ordered the closure of 43 schools in the area Wednesday, but later announced that figure had more than doubled.

"The ministry of education has decided to close all 111 schools in the Pasir Gudang area immediately," he said in a statement.

"The education ministry is requesting that all parties take precautions."

Three men were arrested earlier this week over the toxic waste dumping. One is expected to be charged in court soon and could face up to five years in jail if found guilty of breaking environmental protection laws. (AFP)

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