Poor visibility forced two Dumai-bound flights to return to Pekanbaru on Monday morning as the haze from nearby forest fires returned to shroud the Indonesian coastal city.
Riau province has seen a fresh spike in the number of forest fires in recent days.
Satellite readings showed 173 hotspots on Sunday in Riau, about 280 km from Singapore, a sharp jump from just 63 hotspots on Saturday.
The airport in Dumai was closed for more than a week at the height of last month's haze.
"Around 10.30am, visibility at Pinang Kampai airport dropped to 500 metres, below the standard visibility of 4,000 metres during normal weather," said head of Pinang Kampai airport Mr Catur Hargowo.
Dumai recorded a PSI level of 175 at 11 am, though the reading is expected to fall later in the day due to strong winds.
Still, Mr Marjoko Santoso, head of Dumai's health department, warned: "With the deteriorating condition, we appeal to all residents to wear masks during outdoor activity."
Parts of Malaysia, including Malacca, rural Selangor, parts of Negri Sembilan and Muar, have also seen worsening haze conditions since this morning.
Visibility as of 2pm have plunged to less than 4km in Batu Pahat (Johor), Kuantan (Pahang), and the major urban centres of Petaling Jaya, Sepang and Subang.
Visibility in capital city Kuala Lumpur has also declined since this morning.
The Malaysian Meteorological Department in a statement said to expect two to three days of haze following change in wind direction due to the south-west monsoon, forecasted to last until September.