Workers discovered numerous bones during earthworks at Clontarf Reserve at lunchtime on Thursday, with police called to the site at 12.15pm.

"Officers attached to Northern Beaches Police Area Command attended and a crime scene was established," a NSW Police spokeswoman said.

"The remains were seized by police and will undergo forensic examination to determine if they are human and their origin."

The NSW Police spokeswoman would not confirm how many bones were discovered, how big they were, or if a skull was among them.

Works at the site were being conducted as part of Northern Beaches Council's Clontarf Reserve Masterplan to upgrade the playground.

Shade sails, swings and some playground has already been installed at the site, with works expected to be competed in late November.

IN OTHER NEWS:

A day after the bones were found, the worksite remains shut and fenced off to the public.

Northern Beaches Council has been contacted for comment.

More to come.