Japan's big three automakers enjoyed soaring net profits in the last business year, but analysts warn it is too early to say the robust results suggest a return to their glory days.

The analysts said the strong earnings mostly stemmed from transient factors such as a favorable foreign exchange and tax cuts.

On Monday, Nissan Motor Co. announced its net profit rose 12.6 percent to ¥746.9 billion for the business year that ended in March.