Tokyo, Sept. 29 -- Asian stocks were mixed on Tuesday after Wall Street recovered some of this month's losses as investors looked ahead to a debate between President Donald Trump and his challenger in the November election, former vice president Joe Biden.

Shanghai and Seoul advanced while Tokyo and Hong Kong declined. Sydney was little-changed.

Overnight, Wall Street's benchmark S&P 500 index gained 1.6%, led by big tech stocks.

This is welcome cheer, but does not redeem equities from a negative September, Mizuho Bank said in a report. Its analysts questioned whether, without an obvious catalyst, the rise was driven by little more than month-end short-covering, or traders buying stocks to fulfill commitments to re-sell them.

The Shan...