Toyota Motor Corp. and Nissan Motor Co. may forecast first-half losses as Japan's two biggest carmakers struggle to restore full production disrupted by the nation's record earthquake.

Toyota may post net losses of ¥155 billion in the three months ending June 30 and ¥241 billion for the six months ending Sept. 30, according to the average of analyst estimates compiled by Bloomberg in the past four weeks. Nissan's six-month net loss may be ¥48 billion, based on the estimates.

In the worst case, combined losses for the nation's carmakers and suppliers may be "the biggest ever," surpassing those at the time of the 2008 to 2009 financial crisis, Noriyuki Matsushima, an analyst in Tokyo at Citigroup Inc., said last week. Citigroup also downgraded Japan's auto industry to "sell" from "buy" on April 8.