Three major property and casualty insurance groups reported robust earnings growth for the first half of the 2013 business year due to greater investment returns amid the surging stock market.

MS&AD Insurance Group Holdings Inc. swung into the black in the April-September period with a consolidated net profit of ¥109.57 billion against a year-before loss of ¥9.44 billion.

NKSJ Holdings Inc. also returned to the black with a net profit of ¥29.17 billion against a loss of ¥37.33 billion. Tokio Marine Holdings Inc. saw net profit jump 46.2 percent to ¥91.43 billion.

Net premium income increased 6.2 percent to ¥1.42 trillion at MS&AD, 13.1 percent to ¥1.42 trillion at Tokio and 7.7 percent to ¥1.12 trillion at NKSJ as their respective overseas affiliates saw a boost in such income.

The groups are concerned that the auto insurance business environment will deteriorate due to the planned consumption tax increase next April that will inflate auto repair costs with no increase planned in premium frees from the sales tax, industry sources said.

"A premium increase will be one of the options," said Managing Director Hirokazu Fujita of Tokio Marine & Nichido Fire Insurance Co., which raised premiums in October.