Six passengers, including a child, were treated for bumps, bruises and other minor injuries, city fire spokesman Brian Humphrey said.
American Airlines Flight 31 to Honolulu, carrying 188 passengers and six crew members, took off from the airport at 8:48 a.m., American spokesman Tim Smith said.
A short time later, the pilot decided to turn back.
"They had some type of smoke or odor in the cabin," Smith said.
The Boeing 757 landed about 57 minutes later and "the captain elected to declare an emergency and get everybody out of the aircraft via the slides," Smith said.
American Airlines spokesman Tim Wagner said airline officials were trying to determine the source of the problem. The airline was to make arrangements for another aircraft to take the passengers to Honolulu, reports CBS station KCBS-TV in Los Angeles.
Fire crews using thermal imaging cameras scanned the cabin and cargo hold "and thus far found no evidence of an active fire," Humphrey said.
He said the airline, the National Transportation and Safety Board and the Federal Aviation Administration will investigate.
The American flight landed as fire crews were preparing for a publicity event at the airport. Fire trucks were supposed to spray streams of water to welcome an Airbus A380 - the world's largest jetliner - flown by Emirates Airlines.
The American emergency landing delayed the Emirates flight for about 45 minutes, and the water cannon ceremony was scrapped, said Erin Franklin, a publicist for the event.