GRAND FORKS, N.D. (AP) _ Workers hurriedly bulldozed a protective levee around this flooded city's only hospital Sunday as patients were evacuated because of a shortage of clean drinking water.

United Hospital set up a 20-bed mobile surgery center at the Grand Forks Air Force Base west of the city, said Rosemary Jacobson, the hospital's president.

Patients also were transferred to hospitals elsewhere in North Dakota, Minnesota and Iowa.

Nurses and hospital workers labored Sunday to pack off movable hospital equipment to the air base.

The Red River, which spilled over dikes protecting the city Saturday, lapped against a 4-foot hospital levee and a separate sandbag dike.

The flood had already overwhelmed Grand Forks' water treatment plant, and city officials said municipal drinkable water may not be available for at least two weeks.

A National Guard water purification unit that had been operating on the hospital's grounds was forced to move elsewhere.

Beginning Saturday, more than 500 people had been moved from the hospital and a nearby nursing home and residential elder care facilities, Jacobson said. The remaining 60 patients, many of whom were on respirators and intravenous systems, were moved by Sunday evening.

The hospital has generators to provide electricity but the lack of clean water would make things difficult, Jacobson said. ``We felt we couldn't provide care to these patients for the very long haul,'' she said.

Some hospital staffers will remain even when all the patients have been relocated.

``We won't lock the doors and leave,'' Jacobson said.