Only five venture-backed companies have gone public this year, prompting market watchers to warn of a growing crisis in the start-up community.

Over the second quarter, not a single venture-backed company filed an initial public offering, the first quarter in 30 years without an IPO, according to a report by the National Venture Capital Association.

By contrast, 43 companies went public by the first half of 2007.

"Venture-backed companies that successfully enter the public markets represent a critical job creation engine for the United States economy, and that engine has completely shut down," Mark Heesen, the New York-based trade group's president, said in a statement.

Venture capital firms are blaming the IPO drought on skittish investors, the credit crunch and mortgage crisis, and tougher regulations under the Sarbanes Oxley Act, the report said. Dixon Doll, the group's chairman, said systemic factors combined with the weaker economy were making IPOs a less attractive source of capital for fast-growing companies.

"Imagine the implications if Genentech, Google, or Intel decided to forgo a public offering and become acquired because the public market option was unappealing," Doll said in a statement. "The next Genentech or Google may be making that decision right now."

The number of mergers and acquisitions is also down, dropping by 28 percent from last year, the report said. The technology sector continued to dominate M&As in the second quarter, accounting for 36 of 50 deals with a disclosed value of $1.8 billion.

Heesen described the latest quarter as the "canary in the coal mine," and urged regulators and legislators to take notice.