Shares of UnitedHealth Group are surging before the market open Friday as Warren Buffett's Berkshire Hathaway disclosed that it recently purchased shares of the beleaguered insurer.

Warren Buffett's Berkshire Hathaway has acquired 5 million shares in UnitedHealth Group , a regulatory filing showed on Thursday, sending the health insurer's stock up 7% in extended trading.

UnitedHealth shares jumped 10 per cent in pre-market trading on Friday after Warren Buffett’s Berkshire Hathaway snapped up a stake in the troubled US healthcare group. The new investment, worth $1.6bn at the end of June, was disclosed in a filing late on Thursday detailing changes to Berkshire’s $268bn stock portfolio during the second quarter.