Google Inc. (GOOG) said a "small subset" of Gmail users were unable to access their accounts on Thursday morning, the second outage to hit the popular email service this month.

The company didn't immediately provide details about the cause or the scope of the outage but said full service was expected to be restored soon. The company acknowledged the issue at about 7:30 a.m. Pacific time (10:30 a.m. ET) and provided readers with a work-around solution to access their accounts.

Google then said on its Gmail help page at 8:29 a.m. PT that service had been restored for some users and that it expected a resolution for all users within an hour. It also said some users might continue to experience problems with their contact lists.

The disruption follows similar issues that have affected Gmail users in recent months. In February, Google mail users around the world were locked out of their accounts for up to 24 hours after the company introduced new software that triggered a bug in the email program's code.

Gmail went down for about an hour and 45 minutes on Sept. 1, during which time users could access their email only through third-party applications such as Microsoft Outlook. A company executive apologized after that incident in a blog post, saying the outage was "a Big Deal."

The latest service glitch, while apparently much smaller than earlier outages, will likely increase concerns about the reliability of Web-based software, which Google is promoting as an alternative to Microsoft Corp.'s (MSFT) packaged products.

Shares in Google were down 0.3% at $497.10 in midday trading.

-By Scott Morrison; Dow Jones Newswires; 415-765-6118; scott.morrison@dowjones.com