Cork County Council, which oversees emergency services, said six people died and six others injured. The Irish Aviation Authority responsible for running the airport said the fog was so thick that air traffic controllers in a nearby tower could not see the crash, only hear it.
Council spokeswoman Kay Keegan said two passengers were cut from the wreckage, and all six survivors - among them passengers with severe burns - were taken to Cork University Hospital.
The Irish Aviation Authority said the aircraft, a turboprop leased to Isle of Man-based airline Manx2.com, aborted two attempts to land before crashing on the third attempt. It had been traveling from Belfast, Northern Ireland.
Authority chief executive Eamonn Brennan said the pilots were trying to land using instruments. He said prevailing winds were weak and not a factor, while Cork frequently suffers from fog.
Brennan said the pilot first tried to land on the southern runway but pulled up, then immediately tried again on the northern runway but aborted that too. He said the pilot waited another 20 minutes, then tried the southern runway again - but landed short.
Brennan said the aircraft hit the very edge of the tarmac and either cartwheeled or flipped into a field beside the runway, catching fire in the process.
"The visibility was so bad that the tower was not in position to see the aircraft when it impacted," he said.
Television footage of the crash scene showed that the aircraft's wings were shorn off and the entire front half of the fuselage was crushed. The wreckage came to rest upside down with the landing gear extended and intact. The tail was protruding upward, with comparatively little external damage evident to the rear seating area of the aircraft.
Brennan said the aircraft was a Fairchild Metroliner, a 19-seat turboprop aircraft manufactured in San Antonio, Texas, in 1992. It was carrying 10 passengers and two crew members.
Cork Airport's runway has been closed and all incoming flights are being diverted to Shannon, the larger airport in southwestern Ireland.
Irish airline Aer Lingus said it has diverted 16 flights to Shannon and canceled four others. Ryanair said it has diverted five flights to Shannon and canceled two others.
The Catholic bishop of Cork, John Buckley, comforted relatives of the dead and injured who had been in the terminal at the time of the crash. Buckley said he "offered them the prayers of all Irish people at this sad time."
Manx2.com was founded in 2006 and operates flights linking Ireland, Britain and the Isle of Man. It opened the Belfast-Cork route six months ago.
Thursday's crash was the deadliest in Irish aviation since 1968, when an Aer Lingus flight from Cork to London crashed into the Irish Sea, killing all 61 on board.
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Online:
Cork Airport, http://www.corkairport.com/tns/home.aspx
