A second US politician has been embroiled in scandal, apologising for wearing blackface to a party in 1980 to impersonate a rapper.

Attorney General Mark Herring is second in line for for the governorship of the state of Virginia, where the Democratic governor and the lieutenant governor are already facing claims of scandal.

Herring, 57, who has served as attorney general since 2014, apologised for what he described as "callous and inexcusable lack of awareness."