Donald Trump has opened up a double-digit lead over Hillary Clinton among registered voters who are active and former military servicemen and women.

A new NBC/SurveyMonkey poll shows the Republican presidential nominee leading his rival by 19 points.

The news comes on the day Trump is set to deliver a speech about military policy, and as the two candidates are sparring over which has the support of more retired generals and admirals.

Fifty-five percent of active and former military members support Trump, while 36 percent back Clinton, according to the new poll, released Wednesday morning.

Republican presidential candidate Donald Trump, shown Tuesday with retired U.S. Army general Michael Flynn in Virginia Beach, Virginia, is far ahead of Hillary Clinton among veterans and active military service members

Clinton, shown Tuesday aboard her campaign airplane, has unveiled a list of 95 retired military flag officers who back her

Trump has opened up a big lead among registered voters who say they have served in the U.S. military at some point

And 64 per cent say they lack confidence in Clinton's ability to be an effective commander-in-chief. Forty-seven percent say the same about Trump.

Military voters also gave Trump a 52-28 edge on his ability to handle veterans issues, a platform that has been part of the Republican's campaign stump speeches for more than a year.

Both candidates will participate in a Commander in Chief forum in New York City on Wednesday night, hosted by Iraq and Afghanistan Veterans of America.

The unprecedented event will air on NBC and MSNBC at 8:00 p.m. Clinton will appear first, following a coin toss, giving Trump the enviable chance to rebut her during the second half of the hour.

They will take questions from NBC's Matt Lauer and an audience full of veterans and active service members.

Clinton unveiled a list of 95 retired generals and admirals on Wednesday who are endorsing her.

That list one-ups Trump's, which included 88.

Trump has made veterans issues a major part of his campaign, and is set to deliver a speech Wednesday morning about military policy

The NBC/SurveyMonkey Weekly Election Tracking Poll samples the opinions of 32,226 adults who fill out surveys on the online platform and say they are registered to vote.

The new numbers are limited to 3.358 registered voters who say they have served in the military at some point.

While SurveyMonkey says it has access to a pool of nearly 3 million Americans, it may not be a representative sample of U.S. voters since less than 1 per cent of the nation's population has any chance at all of being surveyed.

SurveyMonkey itself reports that 'the biggest challenge of non-probability sampling is recreating the same kind of non-biased results that probability sampling gives you.'