Wild weather and poor property maintenance may have played a role in ripping a sheet of metal from a central coast balcony, sending a mother and her baby plunging more than five metres.

Three-month-old Aiden landed head first on the concrete driveway of the ageing Niagara Park rental home and died from head injuries on Sunday evening.

His mother, Colleen McKeon, 43, suffered a suspected broken back in the accident, which has prompted warnings that one in eight balconies have serious structural issues.

Narani Avenue residents said a wild thunderstorm rolled into the area with little warning on Sunday, sending material flying through the street. ''It came up out of nowhere and everyone was running and ducking for cover, most people were trying to get cars in and shut the windows and a bit of tin flew from next door,'' one resident said.

''The next thing I saw was ambulances coming up the road.''

A panel of corrugated iron fell from the second-floor balcony and tore through a protective fly screen, leaving a gaping hole.

Superintendent Daniel Sullivan said the police investigation would focus on the ''structural integrity'' of the 20-year-old rental property, which former tenants have suggested was in poor shape.

Structural engineers, police officers and building inspectors from Gosford City Council inspected the balcony on Monday. The tragedy has prompted calls for regular building checks, particularly in rental properties.

Architect Robert Caulfield, former president of the Royal Australian Institute of Architects and the director of Homesafe Group, estimated one in eight balconies in Australia have maintenance issues "that could cause an injury of some sort".

He said rotting timber balconies were the most problematic but those made of steel could also fail if the fixings rust and detach.

"A balcony by nature is a fairly flimsy structure … it doesn't take a lot of deterioration before they become dangerous," he said.

NSW Fair Trading Commissioner Rod Stowe said balconies should regularly be assessed for deterioration and it was the responsibility of landlords to ensure rental properties were safe.

The owner of the Niagara Park home could not be reached for comment.

Ms McKeon, a mother of five boys, who described her pregnancy as a ''happy'' surprise, moved into the five-bedroom property three months ago.