ALBANY — Electronic unemployment filing systems have crashed in at least three states in recent days amid an unprecedented crush of thousands of newly jobless Americans seeking benefits, and other states were adjusting their systems to avoid being next.

About 4.5 million Americans are collecting jobless benefits, a 26-year high, so the Web sites and phone systems now commonly used to file for benefits are being tested like never before.

Even those that are holding up under the strain are in many cases leaving filers on the line for hours, or kissing them off with an “all circuits are busy” message. Agencies have been scrambling to hire hundreds more workers to handle the calls.

Systems in New York, North Carolina and Ohio were shut down completely by technical glitches and heavy volume, and labor officials in several other states are reporting higher-than-normal use.

“Regardless of when you call, be prepared to wait and just hang on. Try not to get frustrated,” said Howard Cosgrove, a spokesman for the Wisconsin Department of Workforce Development, which boosted its staff of telephone operators by 25 percent last month to cope with a phone system that has been overloaded for weeks. “We sympathize, we’re on their side, we’re doing our best to help them out.”

The nation’s unemployment rate in November zoomed to 6.7 percent, a 15-year high. Economists predict it will rise to 7 percent in December, with another 500,000 jobs probably cut last month. The government releases its monthly employment report on Friday.

Some states attribute the increase in call volume in part to an extension of federal emergency unemployment compensation from 13 weeks to 20 weeks in late November.

More than 54,000 Pennsylvanians had exhausted their federal benefits after 13 weeks by the time that occurred, said David Smith, a spokesman for the Pennsylvania Department of Labor and Industry.

“It really was a perfect storm,” he said.

New York’s phone and Internet claims system started to buckle on Monday afternoon and was out of service completely for the first half of Tuesday while as many as 10,000 people per hour tried to get in, said Leo Rosales, a state Labor Department spokesman.

Although that was an unusually high number of calls, Rosales said it was a software glitch in an authentication system used to verify filers’ identities that caused the system to crash

“It’s designed to handle this volume of calls, but the authentication process didn’t work as it should have,” he said. Rosales said the glitch that caused the shutdown has been fixed, and the agency doesn’t expect any more problems.

About 256,000 people are collecting unemployment in New York, up from about 184,000 at this time last year.

North Carolina’s Web site crashed twice this week under a rush of claims as that state set one-day records for both the amount of benefits paid and the number of transactions.

On Sunday and Monday, the number of North Carolinians trying to sign up online for new or continuing benefits was about triple what it was before the economic slowdown started, according to the state Employment Security Commission.

That volume, together with a phone line problem, overwhelmed the agency’s computers and prevented some people from filing claims.

The system was working again by Monday afternoon after the agency added another server and demand decreased, officials said.

“Right now, everything is back to normal,” agency spokesman Larry Parker said.

Ohio’s unemployment hot line also is being crushed by callers, leaving thousands unable to get through Tuesday and no alternative because the Web site for filing claims also is down, according to Brian Harter, a spokesman for the state Department of Job and Family Services.