Apart from Indonesia, Singapore and Malaysia have also been badly affected by haze.

Indonesian authorities on Thursday urged residents in Riau province on Sumatra island to stay indoors as haze from forest fires reached unhealthy levels.

The pollutant standard index shot to 293 in Dumai district on Wednesday and cases of respiratory infections had been on the rise, said Tjandra Yoga Aditama, the Health Ministry’s director of public health.

A pollutant index reading above 200 is considered very unhealthy.

“I have instructed district health offices to advise residents to reduce outdoor activities and wear masks if necessary,” he said.

Mr. Aditama said four districts in Riau had been the worst-hit but flights to and from the airport on Batam island near Singapore were not affected.

Singapore and Malaysia have also been badly affected by haze from Sumatra’s forest fires, which have been blamed on land clearing operations by plantation owners and accidental peat fires.

In Singapore, air pollution has crossed the “hazardous mark” for the first time in the country’s history.

The city state’s Pollutant Standard Index (PSI) reached a record 321 on Wednesday evening, prompting authorities to issue health warnings.

The PSI reading dropped on Thursday morning to 153.

“We are now at the stage where nobody anywhere in the world should believe that they have a right to pollute, to take short cuts and to make money at the expense of people’s health,” said Vivian Balakrishnan, Singapore’s minister for environment and water resources, in an interview with Straits Times.

Neighbouring Malaysia on Wednesday banned the use of fires to clear land and burn rubbish in three states most seriously affected by the haze.

The environment department said the ban applied to the states of Selangor, Malacca and Johor as the air pollution index in some areas of the states had reached an unhealthy level due to the haze.