A goal to build 16,000 affordable homes over the next three years may be overly optimistic, documents suggest.
Official advice obtained by the National Party suggests just half that number are likely to be built.
Through its KiwiBuild programme, the government wants to deliver 100,000 affordable homes over the next 10 years.
Housing Minister Phil Twyford has said 16,000 of those will be built in the government's first term.
But in the documents, the Ministry of Business, Innovation and Employment estimates only 8000 KiwiBuild homes will be constructed over the next three years.
National Party housing spokesman Michael Woodhouse said Mr Twyford was making big promises that he simply could not back up.
"His own officials are saying he can only deliver 8000 of that 16,000, even with the initiatives that he wants to put in place with things like the KiwiBuild visa," Mr Woodhouse said.
"So I think Mr Twyford needs to be honest with the public of New Zealand and say that his bold hyperbole in opposition simply isn't going to be matched by the reality, otherwise there's going to be deep disappointment."
MBIE's figures suggested it would instead take four years for 16,000 KiwiBuild homes to be delivered, as the programme scales up.
It said 1000 KiwiBuild homes would be built this year, 2000 next year, 5000 in 2020 and 8000 the next.
By 2022 it predicted 12,000 KiwiBuild homes would be being constructed each year.
In a statement, Mr Twyford told RNZ the government had every intention of meeting its three-year target.
"We have been saying for the past six years that KiwiBuild will ramp up to build 16,000 affordable homes over the first three years.
"The opposition can't have been paying attention for the past two parliamentary terms because that's how long Labour has been talking about delivering KiwiBuild in partnership with the private sector."