Hochtief has sent a strong message to Leighton; stepping in, removing the company’s CEO and CFO, and replacing them with its own people.

Chief executive Hamish Tyrwhitt and chief financial officer Peter Gregg are out, while the current chief executive of Hochtief, Marcelino Fernandez Verdes, has taken charge.

Activities at Leighton Holdings have caught the attention of ASIC regulators, who want to know what happened between a surge in share prices last week and a push for increased ownership this week.

Spanish-controlled German firm Hochtief wants to increase its control of the large-scale Australian building group, offering $1.16 billion to boost its already majority share.

The announcement came after a week of Leighton’s stock price going up nearly every day, but Leighton said there was no extra information to explain the sudden jump in price.

ASIC has issued a notice to the firm asking for more information, as it appears that something important was in the works.

Leighton claims that at the time it had no knowledge of any price sensitive information

Hochtief is keen to buy a larger slice of the big builders, still offering above the already increased price.

Reports say Hochtief wants to buy 37.5 per cent of the shares currently owned by Leighton's other shareholders at a price of $22.15 each. The offer is an 18.8 per cent premium over the average price of $18.65 in trading last week.

Leighton shares ended the week trading at $20.72 - a significant increase in just a few days.

The shares jumped another eleven per cent so far this week, after the Hochtief announcement.

If the offer is taken up by all Leighton shareholders, Hochtief will increase its stake from 58.77 per cent to 74.23 per cent.

The German firm says it would want more of its own people on Leighton's board, reflecting their larger stake in the company.

The offer will also require Foreign Investment Review Board approval.