Just after 11.30 this morning, Reuters shares were up by more than 25% to £6.17, which values the business at around £7.8bn.
Reuters said in a statement: "The board of Reuters confirms it has received a preliminary approach from a third party which may or may not lead to an offer being made for Reuters.
"There is no certainty an offer will be made or necessary approvals, including those required under Reuters constitution, will be received."
Under Reuters ownership structure, no shareholder may own 15% or more of Reuters shares and a single "Founders Share", also known as a golden share, can block a hostile bid.
The Founders Share is owned by the Reuters Founders Share Company, a private company run by 15 trustees. If the directors believe that any person, together with any associates, is seeking to obtain or has obtained control of Reuters, they can use the special voting rights they have.