Mortgage rates are likely to rise if the UK quits the European Union, the Chancellor has warned.
Families would be left "paying the price" of a Brexit as instability in financial markets pushed up the cost of repayments, George Osborne insisted.
Experts are "pretty clear" that prices would increase if voters choose to leave the 28-strong bloc in the June 23 referendum, he said.
The International Monetary Fund (IMF) earlier this week warned that quitting could inflict "severe regional and global damage" and downgraded its forecast for UK economic growth.
Mr Osborne said: "If you look at the view of the experts here at the IMF in Washington it's pretty clear that if Britain votes to leave the EU then prices will go up and there will be instability in financial markets. What that means for families is that mortgage rates are likely to go up. In other words, it will be families paying the price if Britain votes to leave the EU and I think it's another reason why, frankly, we are stronger, safer and better off inside the European Union."
Matthew Elliott, chief executive of Vote Leave, said: "Less than 24 hours in and the pro-EU camp are already panicking - resorting to doing down the economy and people's mortgages to intimidate the British public into voting their way."
As campaigning ramped up, leading Leave campaigner Boris Johnson said it would be "hypocritical" for US President Barack Obama to seek to use his upcoming visit to the UK to try to persuade Britain to stay in the European Union.
He said: "I honestly don't mind the idea of him joining the debate. Where we do part company, and where I do mind, is that it is plainly hypocritical for America to urge us to sacrifice control - of our laws, our sovereignty, our money and our democracy - when they would not dream of ever doing the same."
Fellow Brexit campaigner Michael Gove insisted quitting the EU would free up more cash for the NHS as Vote Leave put the service centre stage. It claimed a large chunk of the UK's £10.6bn net contribution to Brussels could be diverted to medical care if Britain quits the EU.
He said: "At the moment, the money we give to the European Union is spent by others, people that we have never elected, never chosen and can't remove. If that money is taken back, then that £50m a day will be spent on British people's priorities and the NHS, of course, is top of the list."
Downing Street insisted that Brexit would mean "less money for the NHS", with Mr Cameron's official spokeswoman saying: "A strong NHS needs a strong economy and the Prime Minister has been very clear that our economy is stronger in the EU."
Health unions blasted Vote Leave's figures as "spurious and outrageously misleading", insisting the NHS's financial woes were made in Whitehall and not Brussels. The Remain camp also wheeled out a big gun, former chancellor Lord (Alistair) Darling.
The Labour peer acknowledged that either side could win the contest. "It is going to be very close.
"Every vote counts."