Four people have died after a small twin-engine plane crashed in woodland in Florida, killing everyone on-board. The tragedy happened as the pilot was trying to land the aircraft at Fort Lauderdale Executive Airport around 4.30pm on Sunday. The unnamed pilot declared an emergency, but the plane crashed shortly after in a wooded area close to the runway, before bursting into flames. Scroll down for video . A 'fireball' exploded after the twin-engine plane crashed in Florida. The reason for the crash is not yet known . Firefighters battled to put out the flames on the crash site. Four people died in the tragic incident on Sunday . The pilot declared an emergency shortly before the plane crashed into a wooded area close to the runway . Eye-witnesses say they knew something was wrong as they watched the Piper PA-31 aircraft coming into land. 'It sounded low, it looked low', Bobby Bemis told NBC in South Florida. 'It nosedived right into the floor. It sounded like a semi truck hit a wall, it was so loud.' Bavon Sylvain said he heard a 'loud explosion, a big fireball'. He added: 'From what we saw, with the fireball, you could tell immediately that whoever was on that plane unfortunately passed away.' The four victims have not been officially named, and it is not known why the plane crashed. Emergency services struggled to reach the scene initially because of the scale of the blaze on the crash site . Emergency services had trouble reaching the crash site because of the size of the fire, and spent Sunday night investigating the scene. Fort Lauderdale Fire Division Chief Chantal Botting.told CBS Miami that there was little left of the plane when the flames were put out. The main cockpit of the vessel is still there, as well as the other adjacent wings and so forth, they are within a remote area,' he said. The four victims of the crash have yet to be named. One runway at the airport was closed for investigators . 'Our crews made an aggressive attack on the fire, extinguishing the fire within minutes. 'Unfortunately, it was discovered there were four souls on board and unfortunately all four perished.' The airport remains open but one runway is closed.
Pilot declared emergency but plane crashed in woodland just off runway .
Everyone on-board the Piper PA-31 aircraft was killed in the tragedy .
Investigators in Florida trying to establish what caused the plane crash .