Sydney - A historic mansion overlooking Sydney Harbour could become Australia's most expensive home, with reports Wednesday saying it could top Aus$100 million (S$118 million).

The Fairfax family, which formerly owned the Sydney Morning Herald, is selling its estate known as "Elaine" which stretches down to a harbour beach in the prestigious eastern Sydney area of Point Piper.

Agent Ken Jacobs, of Christie's International, has declined to put a figure on the price for the seven-bedroom home which includes a ballroom, stables and tennis court and which will go on sale in coming months.

"It's 6,900 square metres of waterfront land on Sydney Harbour and it's in six different titles - there's been no parcel of land come to the market of that size, that's what really sets it apart," he told the ABC.

"It's quite unique, it's the best property ever to come on to the market in Australia."

The estate is several times bigger than Altona, another Point Piper mansion which sold in May for more than $50 million, reportedly to a Chinese buyer.

Buying consultant Stuart Jones, of Rose and Jones, told the Herald that the land and beach frontage would make it worth between $90 million to $112 million.

The property was bought in 1911 by Geoffrey Fairfax for 2,100 pounds.

The record for a Sydney home currently stands as $53 million for another Point Piper mansion, Villa Veneto, while Australia's record is $57.5 million which was paid for a palatial home in the Western Australian capital Perth in 2009.

The Fairfax offering comes in a buoyant market with capital city house prices rising 5.3 per cent in the year to August, according to figures from RP Data-Rismark.

Reserve Bank of Australia assistant governor Malcolm Edey Wednesday warned talk of a housing bubble was "unrealistically alarmist", but said demand for housing was rising.

The RBA has slashed interest rates in recent months to stimulate the economy, with the official cash rate now at a record low of 2.5 per cent.