(New throughout, adds that plant will remain shut, Bonnell market share figures)

June 29 (Reuters) - The casting area of aluminum extruder Bonnell Aluminum's Newnan, Georgia, extrusion plant will remain shut until an investigation into the cause of a Wednesday morning explosion is complete, the company said in a statement.

The blast injured five people and prompted the company to temporarily halt operations at the plant. The rest of the plant besides the casting area will resume operations on Thursday morning, the company said.

One injured employee was airlifted to a hospital in Atlanta, two were taken to a local hospital and two were treated at the scene.

Bonnell, a subsidiary of Tredegar Corp, said it was working with local authorities and state regulators to determine the cause of the 9:15 a.m. EDT (1315 GMT) explosion, adding that a structural engineering firm determined that the rest of the plant was safe to operate following an inspection.

Extrusion is the process of shaping material, such as aluminum, by forcing it to flow through an opening in a die. Bonnell makes extrusions for the building and construction and automotive markets as well as for specialty applications like refrigerators and air conditioners.

Bonnell sold around 77,000 tonnes of aluminum extrusions in 2015, according to Tredegar's full-year results report, released in February. That represented 4.7 percent of total aluminum extrusions shipments in the United States and Canada of about 1.6 million tonnes, according to the Aluminum Association.

A prolonged outage at the plant could reduce the amount of primary and scrap aluminum consumed by the company. This could exacerbate a global glut that has sent prices tumbling about 30 percent from their 2014 peak.

Three-month aluminum on the London Metal Exchange rose 0.7 percent to $1,636.00 per tonne on Wednesday.

A spokeswoman for the Newnan police said it was not a situation involving hazardous materials.

(Reporting by Luc Cohen in New York; Editing by Jeffrey Benkoe)