The lost Dutch/Australian submarine K-IX has re-emerged from her sandy grave at Seal Rocks in NSW thanks to some king tides.

A large section of the submarine has been exposed allowing maritime archaeologists from the NSW Heritage Office a new opportunity to study and record the structure. She appears to be at the levels last seen in 1974 and perhaps in 1989.

"This is an exciting and rare event," NSW Deputy Premier and Minister responsible for Heritage Andrew Refshauge said.

The wreck was relocated by the NSW Heritage Office in 1999 when it was completely covered by sand.

It appeared briefly in mid 2000 after some wave action.

It has not been exposed to its current extent since 1974.

"Submarines are always intriguing archaeological sites," the Minister said.

"The K-IX is of particular interest for its association with the Japanese midget submarine raid on Sydney Harbour on May 31, 1942.

"Then a unit of the Royal Netherlands Navy, the submarine was damaged when an enemy torpedo passed under it and destroyed the ex-ferry Kuttabul, killing 21 sailors on board."

The submarine was later commissioned into the RAN as an anti submarine training vessel.

She was lost while under tow off Seal Rocks towards the end of WW 2.

The Heritage Office has released a shipwreck conservation management plan that documents the discovery of the submarine.

Last year Dr Refshauge unveiled a plaque on a headland near the wreck site outlining the background of the submarine and her loss.

Dr Refshauge also revealed that the NSW Water Police had found another shipwreck in the surf off Blacksmith's Beach, near the entrance to Lake Macquarie.

One possibility is that the hulk is that of the iron paddle steamer, Lowestoft wrecked there in 1864.

Built in the UK, the 29-metre vessel was swamped in high seas while travelling from Newcastle to Sydney.

Heritage Office records indicate there were 24 vessels wrecked near Lake Macquarie and Swansea during the 19th century.

Some 1800 historical wrecks are known to lie in the coastal and inland waters of NSW.