But both surveys also show Pete Buttigieg surging.
And a third poll - released late Friday night - indicates that the South Bend, Ind., mayor edged ahead of Sanders.
Sanders - the populist senator from Vermont who's making his second straight bid for the Democratic nomination - stands at 28 percent among likely Democratic primary voters in a University of New Hampshire survey for CNN.
Buttigieg is at 21 percent support, up 6 percentage points from the previous University of New Hampshire poll, conducted in mid January.
Rep. Tulsi Gabbard of Hawaii is at 6 percent, Sen. Amy Klobuchar of Minnesota's at 5 percent, and billionaire environmental and progressive advocate Tom Steyer and tech entrepreneur Andrew Yang each stand at 3 percent.
Meanwhile, a Suffolk University tracking poll for the Boston Globe and WBZ-TV shows Buttigieg at 25 percent and Sanders at 24 percent support among likely Democratic primary voters in New Hampshire, according to results from Thursday and Friday evenings. Buttigieg has surged 10 percentage points over three nights.
Warren registers at 14 percent, edging up 3 points this week. Biden dropped to 11 percent, down 4 points over the past three nights.
Klobuchar was at 6 percent, Yang at 3 percent, Steyer and Gabbard were each at 2 percent, Sen. Michael Bennet of Colorado was at 1 percent and former Massachusetts Gov. Deval Patrick was at less than 1 percent, the Suffolk poll indicates.
New Hampshire voters are traditionally late deciders and the poll suggested this year is no different. Seven percent said they remained undecided as Tuesday’s primary election nears, and 45 percent of those backing a candidate said they could change their minds before casting their vote.
Earlier Friday, a new NBC News/Marist poll in New Hampshire showed Sanders at 25 percent support, with Buttigieg at 21 percent. Warren stood at 14 percent, with Biden at 13 percent and Klobuchar at 8 percent.
Steyer and Yang each registered at 4 percent, with Gabbard at 3 percent and Bennet and Patrick at 1 percent.
The NBC News/Marist poll was conducted Tuesday-Thursday, with 709 likely Democratic presidential primary voters in New Hampshire questioned by live telephone operators. The survey’s sampling error was plus-or-minus 4.7 percentage points.
The Suffolk University poll interviewed 500 likely Democratic presidential primary voters in the Granite State on Thursday and Friday, using live telephone operators. The sampling error was plus-or-minus 4.4 percentage points.
The CNN/UNH poll interviewed 365 likely Democratic primary voters using live telephone operators. The survey's sampling error is plus or minus 5.1 percentage points.