The vacancy rate in Honolulu’s prime office buildings climbed to 15 percent in the first quarter. If it holds at that level through 2012, the rate would be the highest in 15 years.

Vacancies for so-called Class A buildings haven’t been this high since climbing to 15.1 percent in 1998, according to data released this week by Hawaii Commercial Real Estate LLC. Class A buildings are home to Honolulu’s larger tenants and typically are seen as an indicator of the entire market. The vacancy rate at Class A buildings ended 2011 at 14.4 percent and was at 13.2 percent in the first quarter of 2011.

Waikiki had the highest office market vacancy for both Class A and Class B buildings last quarter at 25.6 percent, while East Hono­lulu had the lowest vacancy rate at 5.4 percent. Class B buildings generally rent for less than Class A and are of a slightly lower quality.

The islandwide vacancy rate for both classes of buildings was 14.6 percent. That compares with 14.4 percent in the fourth quarter and 12.8 percent in the first quarter of 2011.

"While vacancy continued to increase, anecdotal evidence suggests we are near the bottom," the report said. "The numbers of showings are up, and we have seen a number of small startups looking for small space. We have also seen tenants more willing to move, which may suggest that tenants want to lock in good deals now before the market turns."

Goodsill Anderson Quinn & Stifel, one of Honolulu’s largest law firms, recently signed a lease for three floors in the First Hawaiian Center, the report noted.

In the first quarter a net 16,929 square feet of office space became vacant, the smallest amount since late 2009, the report said. In the fourth quarter, a net 54,025 square feet of office space became vacant while that number was 76,185 in the first quarter of 2011.

Of the 10 Oahu submarkets tracked in the survey, three lost occupancy, one remained flat and six markets increased occupancy, the report said.

Downtown was hit hard as it lost 43,091 square feet of occupancy from the fourth quarter and had a vacancy rate of 16.1 percent. The decrease in occupancy came despite a 28,000-square-foot expansion by Honolulu Authority of Rapid Transportation, or HART, at Alii Place.

"It is important to note the cumulative impact of Honolulu’s rail project on downtown office occupancy," the report said. "If the project is killed or stalled, it could mean some or all of the approximately 100,000 square feet occupied by HART and its contractors would come back on the market. Conversely, if the project does get into full swing, more space will be needed downtown."

Class A office vacancy rates have been rising since ending 2009 at 9.8 percent. There were 723,744 square feet of vacancy in Class A buildings at the end of the first quarter.

The Class B office vacancy rate at the end of the first quarter was 14.3 percent, down from 14.4 percent at the end of the fourth quarter but up from 12.4 percent at the end of the first quarter in 2011. There were 924,280 square feet of vacancies in Class B buildings at the end of March.

Gross full-service rents sought by landlords increased last quarter by 4 cents to an average $2.97 a square foot a month from $2.93 at the end of the fourth quarter.