US Vice-President Mike Pence plans to maintain a busy election campaign schedule despite being exposed to a senior aide who has tested positive for Covid-19, his spokesman says.

Donald Trump's running mate will not self-isolate, although he is a close contact of the VP chief of staff, Marc Short.

Mr Pence and his wife both tested negative on Saturday, his office said.

Covid-19 has become a key battleground ahead of the 3 November election.

About 57 million ballots have already been cast in early voting, a record figure largely spurred by the pandemic.

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— Farid Tavos (@tavosfa) October 25, 2020

Mr Pence - who leads the White House Coronavirus Task Force - and his wife, Karen, remained "in good health", his spokesman Devin O'Malley said in a statement.

"While Vice President Pence is considered a close contact with Mr Short, in consultation with the White House Medical Unit, the vice-president will maintain his schedule in accordance with the CDC [Centers for Disease Control and Prevention] guidelines for essential personnel," he added.

Those measures include regular monitoring for symptoms and mask-wearing.

Mr Pence was seen wearing a mask as he returned to Washington DC following a day of campaigning in Florida on Saturday, and after the news of Mr Short's diagnosis was made public, AP news agency reports.

Earlier this month, Democratic vice-presidential candidate Kamala Harris temporarily halted her campaign travel after two members of her staff tested positive. The campaign said it was a precautionary decision as the pair were not considered to be close contacts of the senator.

Meanwhile, media reports say another Pence adviser, Marty Obst, also tested positive recently. The cases have raised questions about White House Covid-19 protocol, three weeks after President Trump was admitted to hospital with the virus before making a recovery.

The vice-president is scheduled to hold a rally on Sunday afternoon in Kinston, North Carolina.