The number of investigations into foreign investors allegedly illegally purchasing Australian homes has more than doubled since June, Federal Treasurer Joe Hockey says.

Mr Hockey said there were now 462 cases under investigation.

He has also confirmed six homes were now for sale because of the Government's crackdown.

"The purchase price of the properties range in value from $152,000 to $1.86 million," he said.

"Some of the five investors have purchased property with Foreign Investment Review Board approval but their circumstances have changed and they have failed to comply with the divestment requirements.

"Some have simply broken the rules."

In June the Federal Government said investigations were underway into 195 cases where foreign investment rules on residential real estate may have been breached.

The probe came a month after the Government announced plans to crackdown on rogue foreign investors amid concerns it was helping fuel property bubbles in Sydney and Melbourne.

While foreign investment laws prohibit foreign investors from purchasing existing residential real estate, they are encouraged to boost the housing supply by investing in new housing developments.

In June the Federal Government announced a grace period until November 30, in which foreign investors who had unlawfully bought established residential property would not be referred for criminal prosecution if they come forward voluntarily.

From December 1, foreign residents who unlawfully bought established property face toughed penalties of up to $127,500 or three years in prison for individuals and up to $637,500 for companies.