Republicans, who now control Congress, have vowed to investigate the matter thoroughly.
ADVERTISEMENTUS President Joe Biden has played down the significance of the second batch of classified documents found in the garage of his house in Delaware.
Biden told reporters at the White House on Thursday that he is "cooperating fully and completely" with a Justice Department investigation into how classified information and government records made their way to his home and the office of his former institute in Washington.
"I'm gonna get a chance to speak on all of this, God willing, soon. But as I said earlier this week, people, and by the way, my Corvette's in a locked garage. Okay, so it's not like you're sitting out in the street," Biden said.
Lawyers found the first set of secret files on 2 November, just days before the midterm elections. But the discoveries were only publicly revealed on Monday.
The revelations have seen Republicans, who now control Congress, pile pressure on the president, and vow to investigate the matter thoroughly.
"You look at President Biden. He wasn't president. He was vice president. He held these in different locations right out in the open," said House Speaker Kevin McCarthy.
"He criticised President Trump. Did he utilise the Justice Department to raid President Trump? Do you think that was right? They knew this was happening to President Biden before the election, but they kept it a secret from the American public."
The Department of Justice is also carrying out an investigation into some 300 classified documents found at former President Donald Trump's Mar-a-Lago estate in Florida.