Emergency rooms at U.S. hospitals are becoming stretched as patient visits increase while the number of emergency facilities declines, a new report said.

Almost two-thirds of hospital emergency rooms in U.S. cities are sometimes crowded, according to the report released Wednesday by the U.S. Centers for Disease Control and Prevention.

“In recent years, growth in the use of hospital emergency medical services (ED’s) has coincided with a decline in the number of EDs, leading to concerns about the capacity of EDs that continue to operate,” said the report.

The annual number of visits to an emergency service rose by 18 percent in the 10 years from 1994, but the number of hospitals operating 24 hours a day decreased by 12 percent over the same time period, it said.

Between 1995 and 2003, the average caseload among operating emergency rooms rose by 78 percent, according to the report.

“Although most of the increase in visits can be explained by growth in the U.S. population, over one-third is accounted for by the growth in per capita use during the last 11 years,” it said.

Nursing vacancies up to 5 percent of staff required, higher patient volume and longer patient waiting and treatment times accounted for the crowding, said the report by the CDC’s National Center for Health Statistics.

Overall, between 40 percent and 50 percent of U.S. hospitals were sometimes crowded, according to the report, which was based on 2003-2004 data.

As a result, almost one-third of U.S. hospitals reported having to divert an ambulance to another emergency department due to overcrowding or staff shortages, the report said.

An average of 4,500 emergency rooms were operating during that period. More than half saw fewer than 20,000 patients annually, but one in 10 had an annual visit volume of more than 50,000 patients, the report said.