A New Year’s Eve campaign shakeup has led at least five aides to Republican presidential candidate Ben Carson to quit the campaign, citing internal tensions.

In the latest sign of trouble within the Carson's campaign, Campaign Manager Barry Bennett and Communications Director Doug Watts unexpectedly resigned Thursday morning amid the one-time top-tier candidate's dropping poll numbers.

Deputy campaign manager Lisa Coen followed Thursday. “I am deeply concerned about the campaign's ability to move forward successfully without them,” she wrote in the letter obtained by NBC News.

Campaign spokesperson Deana Bass tells NBC News that a total of five staffers have left the campaign. Multiple sources close to the campaign say more resignations will come as a result of the shakeup.

“Barry Bennett and I have resigned from the Carson campaign effective immediately,” Watts said in a statement. “We respect the candidate and we have enjoyed helping him go from far back in the field to top tier status. Having just announced raising $23m(illion) for the 4th Q(uarter), more than any other Republican candidate, and passing 1 million contributions and over 600 mm unique donors since March, we are proud of our efforts for Dr. Carson and we wish him and his campaign the best of luck.”

Carson has dropped from leading the Republican field with 29 percent support in a NBC News/Wall Street Journal poll in late October to just 11 percent by the middle of this month.

In a phone interview with NBC News, Bennett blamed acrimony within the campaign on Carson’s close confidante, Armstrong Williams, who is the candidate’s business manager and the man many of his aides say is a central problem in the campaign. Bennett said that he was frustrated that Williams was “undercutting any good news we had” by creating a new problem.

Bennett says he called Carson around 9:45 this morning to notify the former neurosurgeon of his decision. He says the presidential hopeful was surprised and asked him to “take the day to think it over,” but Bennett told NBC News that his mind was made up.

“Some of his advisers just have gotten him to do some things that are not very smart,” Bennett told NBC News in a televised interview to discuss his differences with Williams. “I can't stop them, but you know, I don't need to bang my head on a wall anymore.”

Bennett said the morale of the campaign staff was low and that many staffers felt they were about to be let go over the holidays after Carson hinted of a shakeup. “It was needless, it was pointless,” he said, adding that he hopes the morale returns. “I hope it comes back. I hope that whoever they bring in to replace me can bring it back. But, you know, I think it's beyond my ability to fix.”

Asked if the campaign is a “sinking ship,” Bennett said he remained optimistic. “I don't think so, you know they've got more cash than most, a lot more support than most and

I think he's going to do very well in Iowa. I think we could still win Iowa.”

Williams has been an “ongoing problem since day one,” a separate source familiar with the campaign’s internal workings said, adding that the latest struggles in the polls and in fundraising in the last month are “all self-inflicted wounds created by Armstrong Williams.”

In a brief phone conversation this afternoon, Williams told NBC News he knew Bennett and Watts “had issues with me” but held no ill will towards the two aides, and that he had no influence on the shakeup. “It’s easy to blame. I have nothing but praise for these guys. I knew they had issues with me, we worked around them — it’s like a family,” he said.

Williams also stressed that he wasn’t a large presence around the campaign and that his close relationship with Carson was an issue for Bennett and Watts. “There were challenges, but I’m not a part of the official campaign and I never will be. You know, there’s a lot of trust there [between Dr. Carson and I]; sometimes we don’t see eye-to-eye but we always come to a resolution,” he said.

Carson defended William’s advisory role to reporters in November, telling reporters at the time, “Armstrong is an independent agent, he happens to be a friend of mine, he has nothing to do with the campaign.”

“He does not speak for me, he speaks for himself,” Carson said of Williams, who advocates for Carson on Television regularly.

Last week, Carson suggested in two interviews — conducted without the knowledge of his then-campaign manager— that he has been considering major “personnel changes.” Although he quickly issued a statement, saying he had “100 percent confidence” in his team, Carson said changes were coming.

Following news of the resignations, the Carson campaign released a statement announcing that Bob Dees, a retired U.S. Army Major General Bob Dees who has served as a foreign policy adviser to Carson will take over as the campaign chairman and senior strategist Ed Brookover will become the campaign manager.

“As we enter a new phase of the campaign cycle, it is necessary to invigorate my campaign with a strategy that more aggressively shares my vision and world-view with the American people,” Carson said in the statement. “I commend Barry Bennett and Doug Watts for their efforts to help me share my vision for America. Over a year ago, hundreds of thousands of Americans encouraged me to listen to the call and seek the office of president of the greatest nation the world has ever known. I am ready to be president and believe that my unique experience and background is what is needed to heal, inspire and revive America.”