Chubb Ltd., the global insurer led by Evan Greenberg, is exploring an acquisition of Hartford Financial Services Group Inc. in what could be one of the industry’s biggest deals in years, people familiar with the matter said.

The New York-listed insurer has made a preliminary takeover approach for Hartford, said the people, who asked not to be identified because the discussions are private. Deliberations are at an early stage and may not lead to a transaction, they said.

A representative for Hartford wasn’t able to immediately comment. A representative for Chubb couldn’t be immediately reached for comment.

Shares of Hartford have more than doubled over the past year, giving it a market capitalization of about $23 billion as of Thursday. The stock jumped as much as 12.8% on the Bloomberg News report, and was trading up 12% to $64 at 12:57 p.m. in New York.

Chubb shares have gained 74% during the same period, hitting an all-time high this month and valuing the business at $79 billion. They were little changed Tuesday.

Greenberg Transformation

Greenberg, 66, built the business into a mammoth insurer by combining Ace Ltd., the company he ran, with Chubb Corp. in a nearly $30 billion deal in 2016. The son of former American International Group Inc. CEO Maurice “Hank” Greenberg, he has transformed Chubb into a firm with huge footholds in both personal and commercial lines. The company calls itself the world’s largest publicly traded property and casualty insurer, with operations in 54 countries and more than 30,000 employees, according to its website.

Hartford, led by CEO Chris Swift, traces its roots back more than 200 years. It offers a range of property and casualty insurance including automobile policies, homeowners’ coverage and small business insurance. Hartford reported last month that fourth quarter core earnings rose 22% to $636 million, beating estimates.

The Connecticut-based company ranks as the second-biggest provider of workers compensation insurance in the U.S., according to A.M. Best Co. It also has mutual fund arm with about $139 billion under management, its website shows.

–With assistance from Jan-Henrik Förster, Matthew Monks, Dinesh Nair and Katherine Chiglinsky.