The number of new and existing houses and condominiums sold during the month plummeted nearly 18 percent compared with September 2017, according to CoreLogic. That was the slowest September pace since 2007, when the national housing and mortgage crisis was hitting.

Sales have been falling on an annual basis for much of this year, but this was the biggest annual drop for any month in almost eight years. It was also more than twice the annual drop seen in August.

"The double whammy of higher prices and rising mortgage rates has priced out some would-be buyers and prompted others to take a wait-and-see stance," said Andrew LePage, a CoreLogic analyst, in the release. "There was one caveat to last month's sharp annual sales decline — this September had one less business day for recording transactions. Adjusting for that, the year-over-year decline would be about 13 percent, still the largest in four years."