Satellite images from Indonesia's Riau Meteorology, Geophysics and Climatology Agency showed 113 forest fires in the Indonesian island of Sumatra, causing the haze.
Singapore's air pollution index (API) hit 155 late Monday, the highest since September 1997 when the index reached an all-time high of 226, before easing to 114 on Tuesday.
Singapore's National Environment Agency said the country's air quality was still at an "unhealthy level" as haze with a strong burning smell engulfed the south-east Asian city-state of more than 5 million people.
Singaporean health authorities advised the public, especially children and the elderly with respiratory conditions, to minimize prolonged or heavy outdoor activities.
Singapore has also urged the Indonesian authorities to look into urgent measures to mitigate the occurrences of transboundary haze.
In neighbouring Malaysia, several states were engulfed in moderate haze, prompting Prime Minister Najib Razak to recommend people limit outdoor activities.
Records from Malaysia's Department of Environment showed almost all areas in the peninsular part of the country were enveloped by moderate haze, with four cities having unhealthy levels of pollution.//DPA