By Joshua Kirby 

Shares in Naturgy Energy Group SA surged Thursday after the Spanish utility's shareholders accepted a bid for a stake of just more than 10% from Australia's IFM Global Infrastructure Fund.

At 1419 GMT, shares traded 4.1% higher at EUR23.89, having earlier reached an intraday high of EUR24.87.

In a release filed to Spain's market regulator CNMV, IFM said that its offer of 22.07 euros a share, made via its Luxembourg-based investment vehicle Global Infraco O (2), had been accepted to the equivalent of just more than 105 million shares, or 10.83% of total Naturgy shares. This represents slightly less than half the shares IFM had bid for.

The fund said it had decided to waive the minimum acceptance condition of 17% it had originally stipulated, and would acquire all shares for which its offer had been accepted.

The stake is worth 2.32 billion euros ($2.69 billion), based on the offer price. IFM's original offer, made in January, was for EUR23 a share, but this was later revised downward. The bid was approved by the CNMV in September.

Following the nod from the CNMV last month, Naturgy's largest shareholder said it opposed the bid from IFM. CriteriaCaixa, an investment holding company linked to CaixaBank SA and which holds just more than a quarter of the company's shares, said the move wasn't in Naturgy's long-term interests.

Naturgy declined to comment when contacted by The Wall Street Journal.

Write to Joshua Kirby at joshua.kirby@wsj.com; @joshualeokirby