WASHINGTON (Reuters) - The U.S. unemployment rate unexpectedly shot up to 6.1 percent in August, its highest in nearly five years, as employers cut payrolls for an eighth straight month and labor markets showed signs of accelerating decline.

The Labor Department said 84,000 jobs were lost in August, significantly higher than the 75,000 that economists surveyed by Reuters had forecast. In addition, July's job losses were revised up to 60,000 and June's to 100,000 from a previously reported 51,000 in each month.

Department officials said the August unemployment rate was the highest since September 2003. Analysts had expected the rate to remain steady at July's 5.7 percent rate rather than to jump.

There were steep cuts in hiring in nearly every major category of employment. Some 61,000 manufacturing jobs were lost in August, the most for any month since mid 2003, and 8,000 more construction jobs were cut. There were 53,000 jobs eliminated in professional and business services and 4,000 in leisure and hospitality industries.

The average hours of work remained unchanged from July at 33.7 but employers cut overtime to an average 3.7 hours per week in August from 3.8.

(Reporting by Glenn Somerville, Editing by Andrea Ricci)