"Addressing the national housing crisis is one of the biggest challenges our Government faces," Twyford said.
"The new ministry will provide the focus and capability in the public service to deliver our reform agenda."
It would be the Government's lead adviser on housing and urban development, advising on issues including homelessness, ensuring affordable, warm, safe and dry rental housing in the private and public markets, and support for first home buyers.
Collins said the new ministry would change nothing.
"Phil's just trying to look like he's doing something. He got a big budget allocation of $2 billion in the last Budget.
"So far all we've seen in KiwiBuild is he's going to buy some buildings off the plans from private developers. His interventions so far are not improving the market."
Twyford told Radio New Zealand the move was aimed at providing more houses in a more efficient, capable and accountable way.
He said there was very little capability to deliver KiwiBuild. "We're having to build that pretty much from scratch."
An urban development authority would be established for KiwiBuild and large-scale development projects.
"That would be a powerful delivery agency to speed up the building of housing and these large complex development projects," he said.
Collins said the move would not speed up the delivery of KiwiBuild housing because developers found it difficult to access funding and there was a shortage of skilled tradespeople in the building sector.
"The private sector is now being asked to produce the KiwiBuild houses and dwellings. The trouble that they've got is trying to get the funding but also trying to keep the tradespeople."
Agencies to be brought under the Housing and Urban Development Ministry are:
• The housing and urban policy functions, the KiwiBuild unit and the Community Housing Regulatory Authority from MBIE
• Policy for emergency, transitional and public housing from MSD
• Monitoring of Housing New Zealand and the Tāmaki Redevelopment Company from Treasury