Image copyright Getty Images Image caption Forbes estimates Warren Buffett's fortune at nearly $88bn

Berkshire Hathaway has promoted two long-serving executives as it contemplates a future without billionaire boss Warren Buffett.

The two new vice presidents - Gregory Abel and Ajit Jain - are the potential successors to 87-year-old Mr Buffett who has led the investment firm's expansion.

Mr Buffett said he remains in good health.

He described Mr Abel and Mr Jain as having "Berkshire in their blood".

The promotions are designed to give the two men experience running more of the business.

Mr Abel, 55, currently chief executive of Berkshire Hathaway Energy, has been named as vice chairman for non-insurance business operations.

Mr Jain, 66, Berkshire's top insurance executive, will be vice chairman for insurance operations.

Both were also added to Berkshire's board, expanding it to 14 people.

Mr Buffett told CNBC that the changes should be almost imperceptible from the outside.

"It's part of a movement towards succession over time, and they are the two key figures at Berkshire," he said. "This would have made sense five years ago, too."

He later blamed "lethargy, bordering on sloth" for not making the announcements sooner.

Image copyright AFP/Getty Image caption Warren Buffett has a legendary reputation in China, where his image has graced Cherry Coke bottles

Mr Buffett has led Berkshire Hathaway for more than four decades, turning it into a complex conglomerate with holdings in freight rail, major insurance companies, real estate, newspapers and utilities.

Its investments include Geico, the Kraft Heinz Co, Fruit of the Loom and Acme Brick Company, as well as Northern Powergrid subsidiaries, which serve about 3.9 million customers in the UK.

The firm and its subsidiaries employ more than 367,000 people globally.

The companies are run in a decentralised fashion, but major investment decisions remain controlled by Mr Buffett and vice chairman Charlie Munger, 93.

Mr Buffett said he still goes to the office on Saturdays, but succession planning has long been part of the discussions among Berkshire Hathaway board members.

Mr Buffett said Mr Jain and Mr Abel oversee divisions that are different, but roughly comparable in power and importance

He said they won't be pitted against each other to step into his shoes.

"They know each other well, they like each other well, they both have their areas of specialty," he said.

'Oracle of Omaha'

Mr Buffett's time at Berkshire has vaulted him to the ranks of the world's richest men, with a fortune Forbes estimates at nearly $88bn.

Sometimes called the 'Oracle of Omaha', Mr Buffett is known for his focus on long-term investments and folksy bearing.

He has lived in the same Omaha, Nebraska home for decades and pledged to give his wealth to charity.

Mr Buffett said another 10 years at the firm would be "a long time" but he has no plans to step down yet.

"I love what I do at Berkshire," he said. "It's more fun than I think I could imagine."