Most of Japan's major construction firms Thursday reported increased first-half earnings, due to offsetting flat or shrinking revenue with cost-cutting measures.

Kajima Corp., the country's No. 1 general contractor, said its operating profit rose 11 percent to 18.91 billion yen for the April-September period, while revenue was down 7 percent to 732.66 billion yen.

On an after-tax basis, which includes extraordinary gains and losses, the firm posted a 2.61 billion yen net loss after booking a 15 billion yen charge for the restructuring of its group companies.

The construction market has been suffering from a drop in public works projects.

But major construction firms have been helped by a recent pickup in the private sector, which has led to an increase in the construction of manufacturing facilities.

Shimizu Corp. and Obayashi Corp. on the same day reported strong earnings growth despite flat or negative revenue growth by cutting costs, including not accepting unprofitable projects.

Meanwhile, Kajima said it has asked Kokudo Corp. to buy back its Seibu Railway shares. Kajima bought 2 million shares from Kokudo at 2.2 billion yen.

Kajima and other major contractors are among a number of companies that bought railway shares from Kokudo in what may have constituted insider trading. Kokudo did not tell the buyers potentially damaging information.

Seibu Railway shares plummeted after the firm's false financial reporting came to light last month, causing massive losses for the new shareholders.