Police said the 26-year-old Gateshead man had been celebrating Australia Day with friends at King Edward Park when he decided to attempt the four-to-five-metre dive off the cliff face into a tidal rock pool called Bogey Hole, just before 7pm.

"He's failed to clear the lip of the water's edge," Newcastle Local Area Command duty officer Peter Szaak said.

"He's gone in head first and it seems his head's collided with a rock."

A friend and, later, the first police officer to respond, gave the man CPR before he was flown to John Hunter Hospital in a critical condition, Inspector Szaak said.

A hospital spokeswoman said he was in a serious condition this morning.

Bogey Hole is a popular swimming spot in Newcastle but has been the topic of much public debate over its dangerous state of disrepair, The Herald in Newcastle reported.

A Newcastle coastal masterplan recommended its closure on the basis that authorities would not want to spend money on repairs without a financial return.

Police would not comment on safety issues until an investigation was completed, another Newcastle police duty officer, Inspector Jim McArthur, said.

"There are no safety concerns from our point of view. There are adequate warning signs down there," Inspector McArthur said.