Residents of a New Jersey neighbourhood have found out that the sound of helicopters and explosions that kept them awake was a secret Air Force exercise.

Video taken from the backyard of a Totowa resident's house shows a Blackhawk helicopter hovering overhead while at the same time the community was rocked by piercing explosions at around 10pm.

In the clip caught on Michael Melograno's cellphone he says: 'I have never seen anything like this. There was a Blackhawk helicopter flying right over here.'

The Blackhawk helicopter in the sky above Totowa, New Jersey. Explosions terrified local people

Michael Melograno, who took the video, said his parents thought the neighbourhood was coming under attack

The explosions caused many of the residents in the block to come running out of their houses.

'My parents thought we were under attack,' Melograno later told NorthJersey.com.

The helicopters made two trips at 10 p.m. and a second around midnight during the April 16 exercise.

'First it was explosions and then the chopper was so low that our house was vibrating,' resident Larry Pizzichetta told CBS New York.

Another resident, Mauricio Gallardo said: 'We were scared about that, you know? It happened at night time.'

John Emmolo said his daughter called 911 to find out what was happening, but got no information.

'They said, "Well, you have to talk to state police about it",' he said.

Eventually, they learned members of the U.S. Armed Forces were training in secret for three nights.

They were using the North Jersey Developmental Center, which is due to be redeveloped, for their training.