Concern over the safety of Toyota vehicles veered in a new direction Wednesday after Japanese and U.S. authorities said they are investigating more than 100 complaints of brake malfunctions in the Prius, the world's top-selling hybrid and a model sold more in California than in any other state.

The reported Prius brake failures, which have caused several crashes and appear to predominantly involve the 2010 model, are another disturbing revelation for an automaker already reeling from the recall of more than 5 million cars and trucks.

On top of the Prius problem, U.S. Transportation Secretary Ray LaHood testified Wednesday at a congressional hearing that owners of recalled Toyotas should "stop driving" their vehicle until they are fixed. He later called his remark "obviously a misstatement," but reiterated his concerns about Toyota and said owners should have their cars and trucks checked by a dealer.

Adding to Toyota's woes, LaHood said his department had received new complaints about Toyota electronics and would undertake a broad review, looking into whether automobile engines could be disrupted by electromagnetic interference caused by power lines or other sources.

Toyota has said it investigated its cars for electronic problems and failed to find a single case pointing that direction.

U.S. Rep. Bart Stupak, D-Mich., chairman of the House Energy and Commerce investigative subcommittee, said Wednesday that Toyota officials

would be asked to give his panel a briefing about the Prius, which has been a showcase car for the automaker. And Apple co-founder Steve Wozniak revealed Tuesday that his Prius had accelerated unintentionally, hitting 97 mph on one occasion, because of a problem he associated with the car's cruise control, an issue not subject so far to any formal recall.

The seemingly ceaseless flow of bad news about Toyota has been hard to take for many of its customers, who have been drawn to the company by its reputation for quality. And the revelations have been particularly dismaying for some owners of Priuses, which have been widely hailed for their cutting-edge technology.

"It's very worrisome to me," said 60-year-old Anwar Khan of Santa Clara, who said he works in the semiconductor industry and owns a 2007 Prius. Although he hasn't experienced any braking or acceleration problems with his car, he added, "I'm getting increasingly irate at the obvious blundering that Toyota is engaged in."

But other Prius owners expressed confidence in the vehicle.

"I just love that car," said John Coelho, 76, of Fremont, who owns a 2008 Prius that's given him no trouble.

"I'm not concerned," added 59-year-old Lyn Olson of Aptos, who said she's owned Toyotas for about 15 years and has had a Prius for the past two years. "It's been such a good car so far. I've had no problems."

A Toyota representative said 22 percent of all U.S. Prius sales in 2009 were in California, slightly down from 25 percent in 2008. Moreover, 36 percent of U.S. households with a Prius buy another Prius, according to the automotive market research firm R.L. Polk, which noted that the typical repurchase rate for a car model is 21 percent.

Nonetheless, the Prius — which is in its third generation since being introduced in 1997 — now finds itself swept up in a growing worldwide controversy over the safety of Toyota vehicles.

Although the Prius is not part of the recent 2.3 million-vehicle recall for sticky accelerator pedals, the 2004-2009 Prius was included in a separate recall issued in November for what the automaker termed "the potential risk for floor mat entrapment of accelerator pedals," a problem linked to a number of crashes, some fatal.

So far, the Prius's reported brake problems have not risen to a serious-enough level to warrant a recall. However, Japan's Transport Ministry on Wednesday ordered Toyota to investigate Prius brakes because the agency had received at least 14 reports of the car's brakes malfunctioning since May.

In the U.S., the National Highway Traffic Safety Administration also reportedly has compiled at least 100 reports of Prius brake problems. As a result, the agency said Wednesday that it is "conducting field work to examine the issue. If we have reason to believe there is a safety risk, we will take all necessary steps to protect consumers."

Most of the braking complaints appear to involve the 2010 Prius, whose braking system is designed differently from earlier Prius models. Many drivers experiencing the problem told the federal agency that their vehicle surged forward or was hard to stop after driving over a pothole or other uneven surface.

Mercury News researcher Leigh Poitinger and wire services contributed to this report. Contact Steve Johnson at 408-920-5043.