Emergency crews were called to a Guligal Rd address about 7pm last night when a bobcat, believed to have been used for backyard renovations, fell on the 20-year-old.

Lake Illawarra Police Acting Inspector John Klepzcarek said the man had been sitting watching the renovation work when the accident occurred.

He said police were looking into the possibility soft earth had given way and caused the bobcat to topple over onto the man.

Residents flocked to the usually quiet cul-de-sac, watching as police, ambulance, fire and rescue crews worked to load the man into the ambulance.

Teresa McDonald, who was visiting her sister at a house across the street, said she heard a ‘‘loud crash and banging’’, just minutes before an ambulance arrived at the scene.

‘‘I yelled out to my sister and said ‘did you hear that?’, we thought someone had been hit by a car,’’ she said. ‘‘That was all we heard and then ... an ambulance turned up with all the lights blazing and they just kept coming after that.’’

Neighbour Lee-Ann Charlton said the man’s family had spent the past few months renovating the home, including levelling the backyard.

The man suffered a serious head injury but was conscious when he was airlifted to Royal North Shore hospital about 8pm.

A hospital spokeswoman said the injured man was in a serious but stable condition as of 2pm Monday.

Police established a crime scene and are conducting inquiries today.