US authorities have arrested a US Coast Guard lieutenant who described himself as a white nationalist and had amassed a cache of weapons to "murder innocent civilians on a scale rarely seen in this country," according to court documents.

Christopher Paul Hasson, who is assigned to the Coast Guard Headquarters in Washington and lives in a Maryland suburb, was arrested on Friday on weapons and drugs charges, prosecutors said in court documents.

The prosecutors called Hasson a "domestic terrorist" and said he wrote in a draft email in June 2017: "I am dreaming of a way to kill almost every last person on the earth. I think a plague would be most successful but how do I acquire the needed/ Spanish flu, botulism, anthrax not sure yet but will find something."

A hearing on a motion to detain him pending trial was set for Thursday.

The Office of the Federal Public Defender in Maryland did not immediately respond to a request for comment and the Coast Guard could not immediately be reached for comment.