TOKYO, June 20 (Reuters) - Japanese stocks fell for a second-straight session as investors locked in recent gains, while trading companies surged after billionaire Warren Buffett raised his stakes in the sector.

Tokio Marine Holdings slid 5.12% while Mizuho Financial Group lost 1.71% amid a wide sell-off in insurers and financial companies.

Mitsubishi Corp jumped 2.54%, leading trading houses higher after Buffett's Berkshire Hathaway said after Monday's market close that it added to holdings in the five biggest players in the sector.

Mitsui & Co and Marubeni - also in Buffett's portfolio - rose 1.42% and 0.63%, respectively.

The trading house sector added 0.89% to become the best performer among the Tokyo Stock Exchange's 33 industry sub-indexes.

The broad Topix index fell 0.81% to 2,271.91 as of the midday break. The benchmark Nikkei lost 0.62% to 33,161.94, but the gauge was in the positive territory for parts of the morning due to gains in heavyweight shares.

Trading cues were scarce following a market holiday in the United States and ahead of data on U.S. housing starts due later on Tuesday.

"Technical indicators continue to show signs of short-term overheating," said Maki Sawada, a strategist at Nomura Securities. "Today, in the absence of any special inputs, we are likely to see some selling to lock in profits, especially in sectors and stocks that have been rising conspicuously."

Among Nikkei constituents, 180 companies fell, while just 43 gained. Insurers led decliners, losing 4.05%

McDonald's Holdings Company Japan bucked the trend, rising 0.52% after the hamburger chain said it would raise prices at its urban locations to contend with higher costs for labour and rent. (Reporting by Rocky Swift; Editing by Janane Venkatraman)