In the most competitive real estate market in American history, sales began to stagnate.

The volume of u.s. home transactions fell 1.2% month-on-month in June, the biggest monthly decline since records began in 2012, according to seasonally adjusted data from Redfin Corp. Inventories are at an all-time low, with an average of 14 days on the market, the fastest ever.

Telecommuting and extremely low mortgage rates have sent a large number of buyers to the suburbs and affordable cities of the United States. The median house price rose 25% in June from a year earlier to a record $386888.

"We have entered a new phase of the real estate market," Daryl Fairweather, chief economist of Redfin, said in a statement. "the price rise is beyond the reach of many buyers."

House prices rose year-on-year in all 85 metropolitan areas tracked by Redfin. The biggest increase was in Austin, Texas, at 43%. It was followed by Lake County, Illinois, up 31%, and Phoenix, up 30%.

San Francisco, one of the most expensive cities in the United States, saw the smallest year-on-year increase in house prices, with only 2.6%.