U.S. mortgage rates dropped to a record low, smashing through a previous record set earlier this year, a closely watched mortgage survey showed Thursday.

Interest rates on U.S. 30-year fixed-rate mortgages fell for a fifth consecutive week, averaging 4.71 percent for the week ending Dec. 3, down from the previous week's 4.78 percent, according to a survey released on Thursday by home funding company Freddie Mac.

Freddie Mac started the survey in 1971.

"Low mortgage rates and the cumulative decline in house prices have contributed to an extremely affordable housing market and helped spur home sales this year," Freddie Mac vice president and chief economist Frank Nothaft said in a statement.

Mortgage rates are linked to yields on Treasuries and yields on mortgage-backed securities.