A Southwest Airlines jet carrying 98 passengers from Baltimore-Washington International Airport slid off a runway after landing at Chicago's Midway Airport in heavy snow last night, plowing through a fence and hitting two vehicles on a nearby road. At least one person on the ground was killed, authorities said.

A 6-year-old boy who was in one of the vehicles was pronounced dead at Advocate Christ Medical Center, a hospital spokeswoman told the Associated Press. Seven other people on the ground were hurt, Chicago Department of Aviation spokeswoman Wendy Abrams told the Associated Press. The accident happened at about 8 p.m. Eastern time. The airport had about 7 inches of snow then, but runway conditions were acceptable, Abrams told the Associated Press.

The Federal Aviation Administration and the National Transportation Safety Board said last night they would send investigators to the scene today, but they were unsure how quickly they could get there because of the snow.

The FAA imposed a "ground stop" at Midway after the accident, which effectively prevents aircraft from landing at the airport because of visibility limitations, spokeswoman Laura Brown said.

The Boeing 737-700, with five crew members, came to a halt at Central Avenue and 55th Street after smashing through a fence on the airport's northwest boundary.

Television images of the scene showed the plane's nose gear collapsed and the front of the plane resting on the ground and covered in snow, as emergency and police crew blocked the area to attend to passengers. The exit doors could be seen open, but it was unclear how long it took to evacuate the passengers.

Eleven passengers were taken to a local hospital, Southwest spokeswoman Angela Vargo said early this morning. The remaining passengers were brought to a safe area within the airport.

"Our thoughts and prayers are with all those who have been affected," she said.

The plane's nose was crushed, and a severely damaged engine was on the ground, Chicago Fire Department spokesman Larry Langford told the Associated Press.

"It's unclear when the nose gear collapsed," the FAA's Brown said last night. It may have collapsed when the plane crashed through the fence or earlier, she added.

Unlike an Air France plane that skidded off the runway in Toronto several months ago, the Southwest jet did not burst into flames.

Southwest Flight 1248 left BWI at 6:50 p.m. Eastern time and landed at about 8:15 p.m. after circling the airport for about 35 minutes, Southwest said in a statement on its Web site.

Southwest has found no indications that the aircraft was experiencing a mechanical problem, Vargo said. The plane is relatively new; the airline received it in July 2004, she said.

The airline said it was in "direct contact" with the FAA and the NTSB as they investigate the incident.

Southwest has never had a fatal crash, but the airline did have a similar incident on March 5, 2000, in which a plane overshot the runway upon landing at Burbank-Glendale-Pasadena Airport in Burbank, Calif. The plane plowed through a fence and onto a nearby road, stopping several feet short of a gas station. Two passengers had serious injuries, and 41 passengers had minor injuries.

The NTSB said the probable cause of the Burbank accident was the flight crew's decision to land the plane when it was going too fast.

A Southwest Airlines flight from Baltimore to Chicago slid off a runway as it attempted to land in heavy snow and wind, authorities said.