A Philadelphia election official says more than 27,000 voters had to cast provisional ballots in the city last Tuesday, apparently confirming reports from citizens and election watchdogs that there were an unusual number of glitches at city polling places.

City Commissioner Al Schmidt said the 27,100 provisional ballots is roughly twice as many as were cast in the last presidential election. The number is equal to about 4 percent of the ballots cast using electronic voting machines.

Provisional ballots are paper ballots used when a voter's registration status is in doubt. The ballot is sealed and opened once the voter's status is verified.

Some of the extra demand for provisional ballots may be related to that fact that about 650 voting divisions in Philadelphia have changed location since 2008 to comply with wheelchair accessibility requirements, Schmidt said. Some voters may have shown up at the wrong location and been given provisional ballots rather than being directed to the proper location.

Others, Schmidt said, may have mistakenly thought they were registered after signing an application with a group that either didn't ensure it was properly filled out or never turned it in.

But, he said, other cases are troubling.

"We had reports of people who were longtime registered voters who do not appear in the poll books," Schmidt said. "We do know that that did occur."

Schmidt said the Election Day materials are prepared by a private vendor based on information from a statewide registry of voters, which should include all properly registered Philadelphians. Schmidt said he's contacted state election officials about the issue.

"I asked for their assistance in identifying how and why that would have occurred," he said.

Schmidt said city elections staff will now go through the provisional ballots to verify registrations and count the votes for those properly registered. That task must be completed before the results are to be certified Nov. 27.

Schmidt said he expects that process will yield more information about the kinds of problems that resulted in the unusual number of provisional ballots.