Smoke swept through the airport's Terminal 2 building after a fire broke out in the departure hall, spurring authorities to seal off the area.
Three people were sent to hospital for smoke inhalation, the Singapore Civil Defence Force (SCDF) said on its Facebook page.
"A small fire occurred at the departure hall of Changi Airport Terminal 2. The fire has been extinguished by SCDF," the Singapore Police said in a statement.
Passengers on flights departing from the terminal on this evening "should expect significant delays," airport management said.
More From This Section
Singapore Airlines said it was "working closely with the airport authority and various agencies to ensure flights can be resumed in the shortest time possible".
An AFP reporter at the airport said the scene was generally calm as the departure and arrival halls were evacuated. Airport staff were also seen leaving but there was no panic.
M Ramarao, 36, an Indian software engineer working in Singapore, was set to take a flight back home with his 18- month-old daughter when they were evacuated.
"If it's for one or two hours it's okay, but they shouldn't cancel the flight."
A Russian tourist who identified himself only as Alexander expressed hope his flight to Moscow would not be cancelled.
"They told us that there was smoke at a part of the airport," he told AFP.
More than 58. Million international passengers passed through Changi Airport last year. The airport serves more than 100 airlines flying to some 380 cities worldwide.