MERRIMACK — More than half of the new apartments currently under construction along the Daniel Webster Highway have already been leased.

Gilbert Crossing, which is a John J. Flatley Co. development that is being built next to the Saint-Gobain Performance Plastics plant, will ultimately bring 240 new apartments to the area.

Town planners previously approved the site plan for four out of the five apartment buildings associated with the mixed-use project.

“At this point we have got four buildings that we have under construction,” Kevin Walker of the Flatley Co. told the planning board last week.

About 98 of those 192 apartments currently being built have already been leased, according to Walker. The first apartment building with 48 units was recently issued its occupancy permit and is at full capacity, he said.

“The need is clearly there. It is moving along pretty quickly,” added Walker.

The developer is now asking for several amendments to its previously approved conditional use permit for the project. Walker is asking permission to construct the fifth and final apartment building with a total of 48 apartments prior to the construction of any retail or industrial buildings that are included in the mixed-use plan.

“The town is getting much more bang for its buck with the apartments,” said Walker, adding the net positive fiscal impact for the town with the five apartment buildings is $557,000, or about $110,000 per building.

Chad Branon of Fieldstone Land Consultants said it would be convenient to construct the final apartment building at the same time the other buildings are being erected so that residents will not be disturbed further by the work.

“The development has been quite popular. It is reserving as fast as the buildings are being constructed,” said Branon.

Branon also asked that the conditional use permit be amended to allow for 101,200 square feet of industrial flex space at the front of the complex, as opposed to the originally approved retail and restaurant space; a separate retail area and high-bay industrial building are set to remain in other areas of the parcel’s development.

“I think in evaluating the climate in the market for this area, my client has determined that this would be a very productive use of the property,” Branon said, adding the industrial flex space will hit a larger market of potential users.

Several neighbors who live across the street at the existing Webster Green apartment complex voiced concerns about nearby water contamination, bus stops, traffic congestion and landscaping.

“I am really concerned about how the Daniel Webster Highway has continued to be built up along that corridor,” said Bill Boyd, a town councilor and planning board member. He said the traffic volume on that stretch of roadway at certain times is concerning.

A traffic impact study will need to be conducted as part of the formal site plan application, according to community development director Tim Thompson. In addition, Branon said that off-site improvements will be considered as part of the site plan review, which will address traffic issues.

No decision was made on the proposed amendments to the conditional use permit. The planning board will review the proposal again on Sept. 17.