Doctors are gearing up for a flood of patients affected by the haze, which crossed into the unhealthy range yesterday.
The Raffles Medical chain for example, issued an advisory to clients on Monday, explaining the effects on the young, the elderly and those with chronic medical problems.
Dr Chng Shih Kiat, its Deputy Medical Director, said the haze could cause eye inflammation or conjunctivitis, irritate the throat and cause runny and blocked nose.
People with lung, heart or asthma problems might become breathless and have difficult breathing.
Those whose chronic conditions are aggravated by the haze should see a doctor immediately.