Shares in IT services and consulting company Atos spiked by more than 16% on Thursday after Onepoint said it has built a stake of nearly 10% in its French competitor.

Atos last year rejected a potential acquisition of its Eviden business for an indicative 4.2 billion euros ($4.45 billion) from Onepoint and private equity funds ICG.

"This investment is made in the context of the ongoing reorganisation of the company and its new governance structure, and underscores the strategic dimension of Atos' assets," Onepoint said in a statement late on Wednesday.

A filing with the French market watchdog AMF published on Thursday confirmed Onepoint held a 9.98% stake in Atos.

Shares in Atos were up 13.2% at 0938 GMT, on course for what would be their biggest single-day gain in almost nine months.

Atos welcomed a new "anchor investor", saying it looked forward to a "constructive dialogue" as with all shareholders.

A person close to the deal said the stake-building had made Onepoint the biggest shareholder in Atos, and represented an industrial, strategic and friendly investment which was aimed at preserving the company's strategic assets.

Two other sources close to Atos said Onepoint's investment looked opportunistic, as Atos shares are trading about 55% off their peak price this year of 15.76 euros.

The French company is in the midst of a potential sale of its legacy operations Tech Foundations to Daniel Kretinsky, in a deal that would also see the Czech billionaire take a 7.5% stake in Eviden, which is what would be left of Atos.

Atos has recently undergone numerous governance changes, with the latest being former banker Jean-Pierre Mustier taking over as head of its board of directors.

($1 = 0.9437 euros)

(Reporting by Piotr Lipinski in Gdansk; Additional reporting by Silvia Aloisi and Mathieu Rosemain in Paris; Editing by Jason Neely, Alexander Smith and Jan Harvey)