Food giant Mondelez International has offered to acquire US chocolate giant Hershey, The Wall Street Journal reported Thursday.

Mondelez, whose brands include Cadbury chocolate, sent a letter to Hershey proposing a tie-up, the Journal said, citing people familiar with the matter.

Hershey had a market value of about $21 billion Thursday morning.

Shares of Hershey shot up 17.8 percent to $114.43 and Mondelez advanced 1.8 percent to $43.75 in mid-morning trade.

A deal would require support from the Hershey Trust, which is chartered by the state of Pennsylvania and holds about 80 percent of the common shares in the US chocolate company.

Hershey reported $7.4 billion in sales in 2015, while Mondelez had $29.6 billion in sales.

Founded in 1894 in the Pennsylvania city of the same name, Hershey's best-known brands include Reese's Peanut Butter Cups and Hershey's Kisses. Besides Cadbury, Mondelez brands include Oreo cookies and Ritz crackers.

Mondelez did not have immediate comment and Hershey did not immediately reply to a request for comment.