Retail stores in the shopping districts of major cities across the United States were boarded up on Tuesday over fears there could be unrest as results of the presidential elections start trickling in.

After a summer of nationwide protests against police violence and racism, the boarding up of businesses in several big cities was an extraordinary sight on Election Day in the US.

Workers covered storefronts with plywood panels in cities including Boston, New York, San Francisco, Los Angeles, Chicago and Washington, DC, NPR reported.

Businesses took the measure as a precaution against break-ins that were seen earlier this year, when looters took advantage of a nationwide wave of civil unrest following the police killing of African-American man George Floyd.

In New York City, the Empire State Building, Macy's department store, and the skyscraper that houses the President Donald Trump-favoured Fox News channel were among those that were boarded up.

On Rodeo Drive, one of the most expensive shopping streets in California's Beverly Hills, staff had stripped the display windows at Tiffany & Co. and Van Cleef & Arpels of their jewels and luxury stores disappeared behind plywood.

"While we intend to remain open where possible, out of an abundance of caution the windows of select stores in key cities will be boarded in anticipation of potential election related activity," Tiffany said in a statement to NPR.

Retailer Target also said they were taking precautionary measures, which could include boarding in some locations, "to ensure the safety of our stores".

According to NPR, the guidance issued by Washington DC authorities for businesses did not recommend boarding up for the election, with city officials saying they were not aware of any credible threats of violence as of late last week.