A private helicopter owned by LG Electronics Inc. crashed in dense fog into a high-rise apartment building in southern Seoul on Saturday, killing two pilots, fire fighters said.

The two pilots -- Park In-kyu, 58, and Koh Jong-jin, 37 -- were the only occupants of the chopper that collided into the upper section of the 38-story apartment in the posh Gangnam district, they said.

No one in the apartment or on the ground was hurt, fire fighters and government anti-disaster officials said, adding that most of the residents in the building were evacuated immediately after the accident.

"It seemed that the helicopter lost visibility due to the thick fog," said an official at the National Emergency Management Agency.

The collision broke windows and damaged the outer wall of the building spanning the 21st to 27th floor. According to officials, the building appears to be fine, but a thorough inspection for safety concerns will be conducted soon.

The I-Park building is one of the most expensive apartments in Seoul.

"I heard a helicopter flying and then a massive bang. I thought war broke out," said Cho Hyun-deok, a resident living on the 26th floor of the building. "I was scared as there was a heavy shaking ... It was after I looked out the window later that I learned a helicopter crashed."

Another resident said he saw the helicopter flying before.

"I thought it was going to crash if it keeps going on the path," said the resident, who declined to give his name. "But it flew that way and slammed into the air conditioner outdoor unit of a home on the 24th floor."

The U.S.-made Sikorsky S-76C++ helicopter was almost completely destroyed with only its tail remaining intact. About 300 firefighters and police were sent to the scene to recover the bodies and investigate the accident.

The helicopter, which took off from Gimpo Airport in western Seoul at 8:46 a.m., was on its way to a heliport in Jamsil near the apartment to pick up senior LG officials for a trip to a factory in the southwestern city of Jeonju, according to LG.

 The helicopter received the greenlight for takeoff when it left Gimpo, LG officials said.

Hours before takeoff, however, the chief pilot, Park, had reported to the company that fog was so heavy that passengers may have to travel to Gimpo to take the helicopter. But Park later reported that weather conditions improved and he could fly to Jamsil to pick them up, they said.

Park is a veteran pilot with about 7,000 hours of flight time, LG officials said. Park's son said both his father and the co-pilot Koh had experience of piloting presidential helicopters when they were with the military.

LG bought the helicopter in 2007 and it is one of two choppers the company has, officials said.

Aviation authorities said the helicopter might have deviated from course before trying to make a landing, though the exact cause of the crash is under investigation.

"After flying over the Han River, the helicopter is presumed to have deviated from the path slightly right before" the planned landing at the Jamsil heliport, said Kim Jae-young, head of the Seoul Regional Aviation Administration.

"We can get to know of the exact path the helicopter took when we recover and analyze the black box," he said, referring to the flight data recorder.

The crash marked the first time a helicopter has slammed into a central city building in South Korea. It aroused concerns about the danger of similar accidents as the number of skyscrapers in the capital continues to increase.

"This kind of accident should not take place any more in a city where high-rise buildings densely stand," Seoul Mayor Park Won-soon told reporters. "The Seoul City government plans to craft out measures to prevent recurrences of such accident."

The government said it plans to analyze the black box of the downed chopper that was retrieved from the scene in a bid to find the exact cause of the accident. (Yonhap News)