A major bounce-back for the housing market in June.

Data released Wednesday showed sales of previously owned homes saw a record jump last month - up a whopping 20.7 percent - snapping three straight months of falling sales.

Historically low mortgage rates are fueling home-buying demand. The average 30-year fixed-rate mortgage is sitting below 3 percent, according to mortgage finance agency Freddie Mac. Homebuyers haven't seen rates that low in nearly 50 years.

Economists, however, warn sales can not continue at this speed.

Just look at the labor market for one reason. There are a staggering 32 million Americans collecting unemployment checks, which limits the available pool of possible buyers.

And that number could get worse with many states either scrapping or scaling back reopening their economies.

Reason number two: pricing. The median price for a home continued to rise from a year ago - hitting a record in June of just over $295,000.

And there's a third reason: lack of supply. Available homes on the market have tumbled 18 percent from a year ago, leaving just four months of supply on the market. A six-to-seven month supply is viewed as a healthy market.

Tight supplies are likely to push prices even higher, which could ultimately limit who can move up or move out.