"To have a young person go from zero to actually doing the things that are needed to meet demand, you're talking 10 years."
Both parties have also emphasised recruiting skilled workers from abroad to realise their home-building ambitions.
Williams agreed this needed to be incentivised but it was no easy task given so many attractive propositions in other countries.
The amount a company would have to pay a foreign professional would also drive up the cost of houses.
"The salary costs for an engineer with five years' experience, they're on $90-$100,000 now and they're really hard to get - and they're not as experienced as you'd ideally like," Williams said.
He was also concerned by the lack of coordination between central and local government, which he said often had warring factions that held up progress.
"They often don't actually have a unified position."
Part of the solution lay in freeing up building regulations and shortening consent times. The next Government should also seriously consider building more pre-fabricated homes, Williams said.
Mark Fisher, of Eighty4 Recruitment, said the construction industry recruitment company did not have a single client that was not searching for staff.
"Obviously there's a major shortage in that lower-level labour force as well but the same problem exists in the high-level, more specialist skill sets, he said.
"When every single one of your clients could take multiple people on, I think you're in a desperate time, aren't you?"
National Party Finance Minister Steven Joyce said the housing figures it used had been independently assessed and included in the latest Branz and Pacifecon independent National Construction Pipeline Report.
"This report highlights the progress being made in housing construction as a result of National's ongoing and comprehensive housing plan which has been developed following extensive research by bodies including the Productivity Commission and consultation with stakeholders," Joyce said.
He pointed out the party's plan, which included Special Housing Areas and Resource Management Act reforms to free up land and speed up consents; its fast-tracking of the Auckland Unitary Plan; its $1 billion Housing Infrastructure Fund to assist councils to speed up builds; and the development of public-private infrastructure funding investment tools.
"All of this means more workers are needed," he said. "These will come from new people being trained, people returning to the industry, and skilled workers coming from overseas. We currently have 43,045 apprentices in training and are targeting 50,000 by 2020.
The minister added: "Our responsible, pragmatic approach to immigration allows industries like construction to employ skilled migrant labour to help fill the gaps as the sector grows."
Labour's housing spokesman Phil Twyford outright rejected many of Williams' claims, stating the party had been in constant conversation with the construction and development industry over the past six years.
"Just because the National Government hasn't invested in the workforce doesn't mean we cannot do it," he said.
"A massive home-building programme like KiwiBuild offers the opportunity to scale the industry up and maintain it at a high level over a number of years, allowing us to build the workforce and for companies to scale up and invest in the plant and technology for off-site manufacturing of houses."
He said Williams was right that it took a while to train people from scratch, "but it is never too late to start".
"With all the other policies we will implement - shutting down the tax breaks for speculators, pushing the bright-line out to five years, banning foreign buyers from buying existing homes, and building large numbers of affordable homes - the extra demand caused by construction workers coming here will not have a significant effect [on house prices]."
Labour agreed with the need for more pre-fabricated houses.
Local Government New Zealand, which represents councils across the country, said it had long advocated for a shared plan to address the many factors driving the housing shortage.
"That needs to be agreed between central and local government and key players in the instruction industry."