One day ahead of the next round of primary elections, the candidates remaining in the race for the Democratic presidential nomination - as well as President Donald Trump - are sticking to their schedules despite the rising number of coronavirus cases across the United States.

Senator Bernie Sanders said over the weekend that his campaign is still gauging whether it will become necessary to cancel the large campaign rallies that public health experts say could be breeding grounds that spread the illness.

"Obviously what is most important to us is to protect the health of the American people," Sanders said during one of a series of television interviews on Sunday. "And what I will tell you, we are talking to public health officials all over this country."

"This is an issue that every organsation, every candidate has got to deal with," he said.

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Federal health authorities have been advising older people and those with medical conditions, in particular, to avoid crowded spaces, prompting the cancellation of music and arts festivals and other events around the country.

But that so far hasn’t led Trump or his two remaining major Democratic rivals, Sanders and Joe Biden, to cut back on big campaign events. Each man is in his 70s.

Sanders said "in the best of all possible worlds" the three candidates should probably limit their travel and avoid crowds, "but right now, we’re running as hard as we can".

Primary elections are scheduled Tuesday in Michigan, Idaho, Mississippi, North Dakota, Missouri, and Washington states, the latter an epicentre of the US outbreak. Some 352 delegates of the 1,991 needed to secure the nomination are up for grabs, with Michigan's 125 delegates being the big prize of the day.

On Monday, Sanders was in Detroit, Michigan meeting with public health experts and others to discuss the outbreak. Biden will make stops in the Michigan cities of Grand Rapids and Flint before holding a rally alongside former contenders Kamala Harris and Cory Booker, both of whom endorsed him over the weekend, in Detroit.

The Biden campaign said on Sunday that the former vice president was following the guidance of state and federal health experts on the outbreak, but there were no planned changes to his campaign activities.

Trump spent the weekend fundraising, playing golf, and meeting with the Brazilian president at Mar-a-Lago, his Florida resort. On Monday, he was scheduled to attend another fundraiser in Florida.

Trump campaign communications director Tim Murtaugh said Sunday that the campaign is proceeding as normal. "We announce rallies when we are ready to announce rallies," he said. "The consideration is always the president’s schedule and what states the president wants to target."

Adams, acknowledging Trump’s busy public schedule, said that for many Americans "life can’t stop", and that ultimately the goal was to minimise risk as best as possible.