Japan's retail sales for March plunged 9.7 percent on-year, well below expectations, after last year's sales were front-loaded as shoppers splurged ahead of a sales-tax increase.
Retail sales were expected to fall 7.3 percent, according to a Reuters poll of 17 analysts. The decline follows February's 1.8 percent drop.
"If you look at the larger data points of the past three to six months, they've been pretty bad all around," Joe Zidle, a portfolio strategist at Richard Bernstein Advisors, told CNBC. "If you think about the consumer's importance ... it's 60 percent of the Japanese economy, I think this ratchets up the pressure on the Bank of Japan (BOJ) in order to introduce more stimulus."
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The economy got clobbered when consumers stopped spending following a rise in the nation-wide consumption tax to 8 percent that took effect last April, forcing the government to postpone a second sales tax initially due this October.
"Admittedly, the 9.7 percent year-on-year fall in sales last month overstates the weakness of consumer spending, as it mostly reflected the surge in expenditure a year ago ahead of the sales tax hike," Marcel Thieliant, an economist at Capital Economics, said in a note Tuesday. But he added that the renewed decline suggests private consumption may have fallen for the first time since the sales tax hike.
"It was widely expected that consumption would benefit from the plunge in energy prices. However, households have chosen to save rather than spend the windfall from cheaper oil," he said noting car sales were down 6.0 percent from February, the sharpest drop since September 2012. "Even fuel sales declined despite a small rebound in gasoline prices last month."
In a separate note Monday, Thieliant said he saw a "good chance" the BOJ Gov. Haruhiko Kuroda would surprise markets with more stimulus at its meeting Thursday. Thieliant expects the BOJ will increase its asset purchases to 90 trillion yen ($750 billion) a yen from the current 80 trillion yen.
--Li Anne Wong and Aza Wee contributed to this article.
—By CNBC.Com's Leslie Shaffer; Follow her on Twitter