Bernie Sanders has jumped into a virtual tie with Joe Biden nationally just before the first nominating contests in the 2020 Democratic presidential primary, according to an NBC News/Wall Street Journal poll released Friday.

The Vermont senator has the support of 27% of Democratic primary voters, a 6 percentage point jump from December, the survey found. The former vice president follows closely at 26% — down 2 percentage points from a month ago. Sanders' 1 percentage point edge falls well within the poll's plus-or-minus 4.7 percentage point margin of error.

Sen. Elizabeth Warren, D-Mass., trails with 15%. Former New York Mayor Mike Bloomberg was the first choice of 9% of respondents, leapfrogging former South Bend Mayor Pete Buttigieg, who came in at 7%.

Sen. Amy Klobuchar, D-Minn., and entrepreneur Andrew Yang garnered 5% and 4%, respectively.

The survey, taken Sunday through Wednesday, offers a snapshot of the Democratic presidential race nationally days before Monday's first-in-the-nation Iowa caucuses. Sanders has steadily cut into Biden's lead in averages of U.S. polls, which capture overall voter sentiment but not voting preference in the states that will decide who faces President Donald Trump in November.

The Vermont senator has also seen his support rise in recent polls of tight races in Iowa and New Hampshire, the second nominating state.

Less than half of respondents to the NBC/WSJ survey — 45% — said they would definitely vote for their first choice. Another 27% answered that they would probably vote for the candidate, and an additional 27% said they were just leaning toward their first choice.

About a quarter, or 24%, of Democratic primary voters pick Warren as their second choice. Biden is the second choice of 20% of respondents, followed by Sanders at 15%.

Bloomberg has fueled a climb in national polling averages by spending at least $100 million on a barrage of ads. He did not try to compete in the first four nominating states of Iowa, New Hampshire, Nevada and South Carolina and has instead focused on Texas and other states that vote on Super Tuesday, March 3.

His ads appear to have made an impression: 59% of poll respondents said they remember seeing an ad from Bloomberg on TV or social media. A third said they recalled seeing an ad for billionaire activist Tom Steyer, and 28% said they remembered seeing an ad for Sanders.

The NBC/WSJ poll of 428 Democratic primary voters took place from Jan. 26-29 and has a plus-or-minus 4.7 percentage point margin of error.

Subscribe to CNBC on YouTube.