WASHINGTON (AP) — America’s housing market has grown so overheated as demand outpaces supply that prices keep hitting record highs — and roughly half of all U.S. houses are now selling above their list price.

Two years ago, before the pandemic struck, just a quarter of homes were selling above the sellers’ asking price, according to data from the real estate brokerage Redfin.

New data further illuminated the red-hot nature of the housing market: Prices rose in March at the fastest pace in more than seven years. The S&P CoreLogic Case-Shiller 20-city home price index jumped 13.3% that month compared with a year earlier — the biggest such gain since December 2013. That price surge followed a 12% year-over-year jump in February.

Several factors are driving the seemingly relentless rise in home prices. The pandemic has encouraged more people to seek out the additional space provided by a single-family home. Yet at the same time, COVID-19 discouraged many homeowners from selling and opening up their homes to would-be buyers, thereby shrinking the number of homes for sale.

And mortgage rates remain at historically low levels, with the average rate on a 30-year fixed mortgage around 3%. A year ago, the average was nearly 3.25%.

Investors, including individuals buying second houses and wealthy Wall Street firms, are also buying more homes, intensifying the competition. Investors bought 17% of homes in April, up from 10% a year earlier, according to the National Association of Realtors. The large millennial generation is also increasingly turning toward home-buying.

Daryl Fairweather, chief economist at Redfin, said that demand had been outstripping supply even before the pandemic as developers struggled to build enough new homes. Builders now say that shortages of workers and lumber are limiting their ability to build.