Malaysia has ordered nearly 500 schools and kindergartens to close until Thursday, after dozens of people were hospitalised with symptoms suggesting they breathed toxic fumes, possibly from industrial waste, the second such incident this year.

Students made up the bulk of the 75 people who have suffered breathing difficulties, vomiting and dizziness since last week, after inhaling the fumes, possibly from waste dumped by factories in the southern state of Johor, bordering Singapore.

More than 1,200 people went to hospital in a similar incident in March that led Malaysia to charge several directors of a tyre oil company with illegal dumping of chemical waste.

Prime Minister Mahathir Mohamad vowed to get tough with those responsible.

"It seems like there are factories that are not very concerned about safety and thus, causing the incident to recur," state news agency Bernama quoted him as saying on Tuesday.

"That is why we have to identify those responsible for causing the pollution and take stern action."

A total of 475 schools, kindergartens and other educational institutions will be shut for authorities to tackle the contamination, state education official Azman Adnan said in a statement late on Monday.

Deshsangbad/fh/mmh