Honolulu police said technical troubles caused a 911 outage for about a half an hour this afternoon.

The outage was discovered about 4 p.m. and affected the Honolulu Police Department’s Communications Division. HPD immediately notified Hawaiian Telcom, its vendor, about the issue, HPD said on its website.

A preliminary investigation by Hawaiian Telcom determined the outage was caused by technical issues, HPD said.

Ann Nishida Fry, Hawaiian Telcom spokeswoman, said some calls to HPD were not completed between 4 and 4:30 p.m. today.

She said an initial investigation found the trouble was probably a local power issue within HPD’s building. She said troubleshooters were monitoring the system.

“The HPD would like to apologize for the inconvenience,” the Police Department said, adding that anyone who called 911 during the outage would be called back.