Warren Buffett added to his stock portfolio at Berkshire Hathaway Inc. in a big way after November 8.

"We've, net, bought $US12 billion ($15.9 billion) of common stocks since the election," he said in an interview with Charlie Rose that aired on Friday. Buffett didn't identify the securities that he picked.

Purchases of that magnitude represent a major pickup in activity for Omaha, Nebraska-based Berkshire. During the first nine months of last year, the company bought $US5.2 billion and sold or redeemed roughly $US20 billion worth of stocks, according to a regulatory filing. In 2015, Berkshire bought about $US10 billion of equity securities.

Stocks rallied after Donald Trump was elected US president in November, as investors speculated that the Republican's policies will stimulate the economy. That sentiment cooled some on Monday after the turbulent rollout of an immigration order raised concern that the new administration may follow through with isolationist policies, overshadowing a pro-growth agenda.