Visibility was down to 500 metres at the Sultan Syarief Kasim airport in Riau province early Tuesday, causing delays in several flight arrivals and departures, said airport official Baiquni.
Flights returned to normal at 10:30 am (0330 GMT), he said.
More than 200 schools in Riau's Siak district were closed because of the thick smoke, the head of the local education office, Kadri Yafis, told the state news agency Antara.
"The air is not healthy for children," he said.
Smoke from forest fires on Sumatra is an annual hazard that often affects neighbouring Malaysia, Singapore and Thailand.
DPA