The New South Wales Government has sold off more than 20,000 properties including schools and public housing dwellings since it came into office in 2011, raking in more than $9.1 billion.

The figures were confirmed during a budget estimates hearing, where Finance Minister Victor Dominello was forced to defend the extent of the asset sales.

"It's in the context of $142 billion worth of assets that we've got," Mr Dominello said.

The hearing was told there was another $1 billion of property sales "in the pipeline".

Upper House Labor MP Daniel Mookhey said the government was approaching a situation where 10 per cent of its asset base would be sold off.

NSW Government Minister Victor Dominello defended the asset sales at the hearing. ( ABC News )

Social Housing properties were among the biggest sellers.

Chief Executive of Property NSW Brett Newman said the Department of Family and Community Services had put more than 4,000 social housing dwellings under the hammer.

Mr Newman said more than 200 of those have been at Millers Point, where the sale of social housing has already raised $422 million.

Another 142 properties in the area are yet to be sold.

Mr Newman pointed out that the money raised would bankroll the construction of new social housing.

"All of that is reinvested into new social housing stock," Mr Newman said.

Mr Newman also confirmed that the government had sold more than 380 Department of Education properties.

During the hearing, Mr Mookhey asked Mr Newman to guarantee none of the education properties would have to bought back, given soaring enrolment figures and increasing over-crowding in schools

"I cannot sit here and give you a guarantee that the Department of Education may not need to buy back any asset the Government has previously sold in the past," Mr Newman replied.

"But the way the department usually operates is it actually looks to identify and recycle often surplus parts of properties and under-utilised sites and then it uses those proceeds to go and buy new sites."