US President Joe Biden presented the Medal of Honour to 81-year-old retired Captain Larry Taylor, a helicopter pilot in the Vietnam War, on Tuesday in Washington DC - but the president faced some criticism for removing his mask after his wife's recent COVID-19 diagnosis.

Captain Taylor, whose actions saved the lives of four American soldiers under fire, was recognised with the nation's highest military honour.

"The Medal of Honour is our nation's oldest and highest recognition of valour. Now, when I called Larry to let him know he finally was receiving this recognition, his response was, I thought you had to do something to receive the Medal of Honour,'' said Biden.

''Larry, you sure in hell did something, man. If you ask anyone here, I'm pretty sure they'd say something you did something extraordinary,'' he continued.

However, Biden's decision to unmask faced media criticism, after First Lady Jill Biden reportedly tested positive for COVID-19 the day before.

Biden initially entered the White House event wearing a black face mask but removed it during the prayer portion of the ceremony, as footage shows. He did not replace it while standing beside Captain Taylor during the Medal of Honour presentation.

Local media did report that the president tested negative for COVID-19 on both Monday night and Tuesday morning, displaying no symptoms.

Earlier, the White House claimed Biden would wear a mask but could remove it when standing at a distance from others.

According to the Centers for Disease Control and Prevention, those exposed to COVID-19 should wear a mask and monitor for symptoms for 10 days,