Bernie Sanders has erased Hillary Clinton's wide-lead for the Democratic presidential nomination, according to a new Reuters/Ipsos poll.

Ms Clinton still leads Mr Sanders 48 to 45 per cent among Democratic voters, after a strong showing in the Iowa caucuses. The survey polled 512 Americans on February 2 through 5.

The poll has a credibility interval of 5 percentage points.

The former secretary of state narrowly beat the Vermont senator in the Iowa caucuses but is expected to lose to him in New Hampshire. The two rivals clashed on Thursday night in their first one-on-one debate, reflecting the tightness of the race.

Nearly a quarter of Democrats and two-fifths of Independents say they are still not that familiar with Sanders. In comparison, Clinton has almost total name recognition among voters.