WASHINGTON, Sept. 16 (Xinhua) -- U.S. homebuilder confidence hit an all-time high in September as historically low mortgage rates continue to boost the housing market, the National Association of Home builders (NAHB) said Wednesday.

The latest NAHB/Wells Fargo Housing Market Index, a measure of the builder confidence for newly-built single-family homes, rose five points to 83 in September, marking the highest reading in the survey's 35-year history.

"The suburban shift for home building is keeping builders busy, supported on the demand side by low interest rates," said NAHB chief economist Robert Dietz.

"In another sign of this growing trend, builders in other parts of the country have reported receiving calls from customers in high-density markets asking about relocating," he said.

However, builders remain concerned about rising costs and delays for building materials, especially lumber, according to NAHB Chairman Chuck Fowke.

"More domestic lumber production or tariff relief is needed to avoid a slowdown in the market in the coming months," Fowke said.

Despite the COVID-19 pandemic, the housing market has become a bright spot in the U.S. economy due to record-low borrowing costs, with homebuilding and purchase activity surging in recent months.

The 30-year fixed-rate mortgage averaged 2.86 percent last week, hitting another record low, according to U.S. mortgage finance firm Freddie Mac.