An FBI search of US President Joe Biden's home has turned up six additional documents containing classification markings, with agents also taking possession of some of his notes, the president's lawyer says.

Bob Bauer, the president's personal lawyer, said the search of the entire premises in Wilmington, Delaware on Friday lasted nearly 13 hours.

The documents with classification markings spanned Mr Biden's time in the Senate and the vice-presidency, while the notes dated to his time as vice-president.

The search came more than a week after Mr Biden's attorneys found six other classified documents in the president's home library from his time as vice-president, and nearly three months after lawyers found a small number of classified records at his former offices at the Penn Biden Center in Washington.

On Thursday, Mr Biden maintained that "there's no there there" on the document discoveries, which have become a political headache for the president and complicated the Justice Department's probe into former president Donald Trump's retention of classified documents and official records after he left office.

"We found a handful of documents were filed in the wrong place," Mr Biden told reporters who questioned him during a tour of the damage from storms in California.

"We immediately turned them over to the Archives and the Justice Department."

Mr Biden said he was "fully cooperating and looking forward to getting this resolved quickly."

The president and first lady Jill Biden were not at the home when it was searched. They were spending the weekend at their home in Rehoboth Beach, Delaware.

Mr Bauer said the FBI requested that the White House not comment on the search before it was conducted, and that Mr Biden's personal and White House attorneys were present.

The FBI, he added, "had full access to the president's home, including personally handwritten notes, files, papers, binders, memorabilia, to-do lists, schedules, and reminders going back decades."