Federal Aviation Administration spokesman Ian Gregor said the smell was reported when the plane was about 25 miles east of the airport. The captain declared an emergency, and the FAA expedited the landing.
The fire department was notified of the situation at 10:21 a.m., and firefighters positioned themselves to meet the plane at its landing spot, a fire dispatcher said.
The flight touched down around 10:30 a.m.
Southwest Airlines spokesman Paul Flaningan said Flight 2433 took off from Las Vegas this morning and was approaching San Jose when people on board "started smelling a smoky smell in the cabin."
He said there was no smoke visible, and that the plane landed without incident and taxied to the gate. Flaningan said there were about 99 people on board and no injuries were reported.
The plane is now being examined to see what caused the smell, he said.
"It's been pulled from service to determine what that was," he said.
Airport spokeswoman Vicki Day said at about 10:40 a.m. that the passengers were deplaning at the gate.
San Jose fire Capt. Mary Gutierrez said about 20 firefighters will remain at the scene as investigators go through the belly of the plane to help determine what happened.
The FAA will work with Southwest Airlines to determine what caused the smoke smell, Gregor said.
