Bail denied for Sydney man who allegedly had homemade bomb under bed

A Sydney man has been denied bail after an explosive device was discovered underneath his bed which prosecutors said had 50 ball bearings or sinkers wrapped around it.

Harley Turnbull pleaded not guilty today to charges related to the discovery of the homemade bomb in his Werrington home on Tuesday night.

Police were called to the 23-year-old's home at about 10.30pm when his mother found the device under her son's bed.

Turnbull said he thought the device was just a firework he bought from a stranger.

The cylindrical device was later detonated by bomb squad specialists at a nearby football field.

Today prosecutors opposed bail, claiming the device was wrapped in either ball bearings or sinkers.

His lawyer, Brad Mallinson, told the court he had entered pleas of not guilty to the charges on his client's behalf.

In arguing for bail, Mr Mallinson conceded Turnbull faced serious offences, had failed to attend court in the past, and possessed a "dreadful" criminal record, mostly related to drug and property matters.

But he said his client "categorically denied" the crown's assertion he planned to take an improvised explosive device containing ball bearings to a public place "as a conversation starter", saying his client did not know "what he was in possession of".

Opposing bail, police prosecutor Ben Seabury said he held "grave concerns" for the community if Turnbull were released, describing the possible injuries sustained if the device had been detonated as "catastrophic".

Magistrate Dorelle Pinch heard the matter.