NEW YORK (AFP) -- Donald Trump sought to reboot his  flagging presidential bid Friday, dismissing his tainted campaign chairman and seeking to broaden his shrinking support base by appealing to black voters and  visiting flood-ravaged Louisiana.

The resignation of the seasoned Republican strategist Paul Manafort -- under fire for his pro-Kremlin ties and role in a Ukrainian corruption scandal -- represents the Republican nominee's latest effort to get back on track after weeks of crisis.

"This morning, Paul Manafort offered, and I accepted, his resignation from the campaign," Trump said in a statement, thanking him for "his great work" and  proclaiming him a "true professional."

Earlier in the week Trump appointed Steve Bannon, a right-wing news executive, as CEO and promoted pollster Kellyanne Conway to campaign manager, in what has signaled a marked new tone following colossal missteps.

Trump shocked many on Thursday by expressing "regret" for past mistakes, and began airing his first television ads on Friday in a desperate attempt to chip into Democratic rival Hillary Clinton's yawning lead in the polls.

The New York billionaire followed up by touring a flood-ravaged region of Louisiana, where officials say more than 86,000 people so far have registered for federal aid and 13 people have died.

Clinton took to Facebook to explain her own absence by saying that while  her "heart breaks" for Louisiana, "right now the relief effort can't afford any distractions." Local Democratic officials had opposed Trump's visit, saying it was wrong to divert valuable manpower.

But others in the state have complained that President Barack Obama, currently on holiday in the exclusive New England resort of Martha's Vineyard, has not visited. He is due to arrive next week.