US Vice President Mike Pence did not wear a face mask during a Tuesday visit to the Mayo Clinic, violating the prestigious medical centre's policy despite his team being warned in advance, AFP reports.

The Minnesota-based centre's policy states: "Part of our protocol for ensuring your safety is to require all patients, visitors and staff to wear a face covering or mask while at Mayo Clinic to guard against transmission of Covid-19."

The clinic said in a statement that it had "shared the masking policy with the VP's office".