Three corporate behemoths — Amazon, Berkshire Hathaway and JPMorgan Chase — announced on 30 January that they will form an independent health-care company for their employees in the United States.

The alliance is regarded as a sign of just how frustrated American businesses are with the nation’s health care system and the rapidly spiralling cost of medical treatment.

It will also cause further turmoil in an industry reeling from attempts by new players to attack a notoriously inefficient, intractable web of medical practitioners, hospitals, insurers and pharmaceutical companies.

It is not clear how extensively the three partners will overhaul their employees’ existing health coverage — whether they would simply help workers find a local doctor, steer employees to online medical advice or use their muscle to negotiate lower prices for drugs and procedures.

While the alliance will apply only to their employees, the three corporations are so closely watched that whatever successes they have could become models for other businesses.

Major employers, from Walmart to Caterpillar, have tried for years to tackle the high costs and complexity of health care, and have grown increasingly frustrated as Congress has deadlocked over the issue, leaving many of the thorniest issues to private industry. About 151 million Americans get their health insurance from an employer.

But the 30-January announcement landed like a thunderclap — sending stocks for insurers and other major health companies tumbling. Shares of health-care companies plunged on that day, dragging down the broader stock market.