Smurfit Kappa Group rejected an unsolicited takeover bid from U.S. rival International Paper in the latest sign of accelerating global consolidation in the booming packaging business.

The cash-and-shares proposal “fails entirely” to reflect growth prospects, said the Dublin-based maker of cardboard boxes and paper bags, without disclosing the terms. Smurfit shares soared as much as 20 percent, the biggest intraday gain in almost a decade, giving a market value of about $10 billion.

“This would be an extremely large deal,” Goodbody Stockbrokers analyst David O’Brien said by phone from Dublin. “Overnight you’d create the top producer of containerboard in Europe, North America and South America.”

International Paper operates a corrugated packaging facility in Auburn on Allied Road where it has historically employed more than 100 people.

A successful acquisition of Smurfit would continue a wave of consolidation in an industry where demand for packaging has soared on global economic growth and the rise in internet shopping. Earlier this year, U.S. producer WestRock Co. agreed to buy KapStone Paper & Packaging for about $3.4 billion, while South Africa’s Mondi Ltd. and DS Smith Plc of the U.K. have both completed deals in the past six months. Mondi stock rose as much as 5.9 percent on Tuesday while DS Smith jumped as much as 9.1 percent.

International Paper makes one in three cardboard boxes in the U.S. and a purchase of Smurfit would see it take over the no. 1 producer in Europe. The offer is “fundamentally opportunistic” and “significantly undervalues” the group, the Irish company said in a statement. Smurfit plans about 1.6 billion euros in capital investment for internal and external growth and is committed to steady acceleration of dividend payments.

Smurfit has a market value of 8.2 billion euros. A spokesman for International Paper said the Memphis, Tennessee-based company had no immediate comment on its offer.

The Irish company has about 46,000 employees across 35 countries in Europe and the Americas and had sales of 8.6 billion euros in 2017. International Paper is currently the right size, Chief Executive Officer Mark Sutton said in an interview last month. It’s valued at about $24 billion.

“This is not likely to be the end of the game, speculation will build from here,” said Gerard Moore, an analyst at Investec in the Irish capital. “If the deal had happened, or does happen, it would be transformational for the industry.”