Baidu.com (BIDU) shares plunged as much as 21 percent Wednesday after two of the investment banks that managed the Chinese Internet company's meteoric initial public offering said the stock price was overblown.

Goldman Sachs (GS) and Piper Jaffray (search) both rated the stock "underperform," given its extraordinary debut on Aug. 5, when it rose more than fourfold.

The eagerly anticipated IPO of Baidu, known as the Chinese Google (GOOG), recalled the dot-com heyday, when first-day price rise records were broken weekly.

The debut of China's lt of critiques over its valuation has surfaced since then.

"Baidu's current stock price has far exceeded even the most aggressive valuations and is distinctly 'off the chart,' in our view," Piper analyst Safa Rashtchy said in a note to clients. He set a price target of $45 on the stock.

Piper Jaffray estimated Baidu is currently trading at about 123 times 2006 earnings before interest, tax, depreciation and amortization, compared with a range of 14 to 26 for its peer group. "We believe this level of disparity is not sustainable and the stock is likely to correct this," Rashtchy wrote.

Baidu shares traded on Nasdaq more than $26 lower at $87.22 after closing Tuesday at $113.59. They were trading at $91.11, down 20 percent, near midday.

"Valuation remains the one downside to the story as we are not able to justify current valuation even when evaluating more aggressive scenarios," Goldman analyst Anthony Noto said in his note initiating coverage. His model valuation on the stock implies a price of about $27, he said.

Baidu, which reported second-quarter revenue rose nearly 200 percent from a year earlier, has already started adjusting market perception. It told investors that third-quarter revenue would rise at a slower rate than previously expected compared with the second quarter.