Quitting the European Union would cause an "economic rupture" with "disastrous" consequences for families, a Cabinet minister has warned.
Brexit is a "reckless" move that would lead to factory closures, an exodus of businesses and job losses, Stephen Crabb said.
Writing in The Sunday Telegraph, the Work and Pensions Secretary warned of the "self-harm" that a vote to leave would cause.
"Lost jobs and livelihoods take an enormous, indelible toll on families and communities," he said. "No one should be complacent about the potential consequences for working people and their families if Britain votes to exit the EU. This is not a theoretical debate."
He added: "When those who want Britain to leave the EU complacently wave away expert predictions of an economic shock, or casually dismiss the warnings of British businesses that employ millions of workers, I think about what that would mean for families who are striving day by day to improve their circumstances.
"And I am troubled by how relaxed they are about the real life consequences of the economic rupture that is at the heart of their position."
The comments come in the first official weekend of campaigning ahead of the referendum on June 23.
Leave supporter Boris Johnson launched a fresh attack on David Cameron for "shamefully" spending £9.3 million of taxpayers' cash on a pro-EU leaflet.
London's mayor rounded on the "scare" tactics of the remain campaign as he completed his northern "Brexit blitz" tour.
In a swipe at the Prime Minister, Mr Johnson attacked those who were "shamefully spending £9.3m of taxpayers' money on a leaflet trying to scare everybody into remaining in the EU".
"In the scare tactics of project fear they are woefully underestimating this country and its people and what we can do."