The annualized rate of new homes sales fell 12.4% in July to a seasonally adjusted rate of 276,600 a year, according to the US Commerce Department.
That makes it the slowest rate since records began in 1963.
A sharp drop in sales of existing homes, the National Association of Realtors also reported on Tuesday.
Analysts fear the data could reflect the weakness in the US economy.
The annualized rate represents what the total number of sales would be if the relative pace for that month were maintained for 12 consecutive months.
Although most analysts had expected a fall in sales, the number was even weaker than expected.
“There is nothing good you can say about the number,” said Steven Ricchiuto, chief economist at Mizuho Securities in New York.
The odds of the dreaded double-dip recession are still increasing.