Wilmington-based Coldwell Banker Sea Coast Advantage is expanding its presence in Onslow County.

The real estate brokerage firm has partnered up with Fayetteville-based homebuilder H&H Homes for a joint office in Jacksonville to tap into what company officials are calling one of the fastest-growing markets in the state.

Officials with both companies broke ground this week on the new building, which will be 12,000 square feet when completed and located on Western Boulevard.

H&H Homes now has eight neighborhoods under development in the Jacksonville area, including five represented by Sea Coast Advantage, according to a press release.

Besides serving as the Jacksonville/Onslow County headquarters for Coldwell Banker Sea Coast Advantage and H&H Homes, the building also is slated to house Alpha Mortgage, Baker & Colby, Sea Coast Properties and Brewed Awakenings as tenants.

The building is expected to be done by October.

More than 50 Sea Coast Advantage agents and support staff will work out of the new facility, doubling the firm’s presence in that area, said Tim Milam, president of Sea Coast Advantage.

Sea Coast Advantage broker-in-charge Carmen Wilkinson said the real estate company led the Jacksonville/Onslow market last year with more than $125.9 million in residential sales, representing a market share of 10.8 percent.

“Jacksonville and Onslow County are critically important in our company’s long-range expansion plans, and we are determined to build on our position as the top-ranked real estate brokerage firm in the area,” Milam said in a statement.