Mr Trump spoke at the Economic Club of Detroit after holding rallies in Pennsylvania on Wednesday.
Meanwhile, Ms Harris attended a Univision town hall in Las Vegas and an evening rally in Phoenix while remaining in close contact with the White House and monitoring federal disaster response efforts.
US President Joe Biden, who said Milton “is looking like the storm of the century”, postponed a trip to Germany and Angola to cope with its aftermath.
Even amid the hurricane, both the Harris and Trump campaigns are using their travel strategically, trying to increase support with key voting blocs who could decide an election expected to be exceedingly close.
Mr Trump has emphasised picking up votes in heavily Hispanic parts of Pennsylvania, including Reading, where he held a rally on Wednesday.
Ms Harris is out west as her campaign looks to increase support among Hispanic voters there, especially men.
Her campaign began a group this week known as “Hombres con Harris”.
Former president Barack Obama is also hitting the campaign trail on Thursday night, making his first appearance for Ms Harris at a rally in Pittsburgh.
That begins what the Harris campaign says will be a series of campaign stops Mr Obama will make on the vice president’s behalf.
Mr Biden spent Monday campaigning in suburban Philadelphia, but has made just one joint appearance with Harris, joining her in Pittsburgh on Labour Day, since he announced he was leaving the race and endorsing her in July.
Mr Obama was among the key Democrats who were part of a behind-the-scenes effort to encourage Mr Biden, his former vice president, to drop out.
Mr Obama and Ms Harris have also been friends for two decades, since he ran for Senate in Illinois.
She campaigned for him when he sought the presidency in 2008.
