ACTON — Five people were hurt Wednesday during an explosion and fire at the Haartz Corp. building on Hayward Road in Acton, the company said.

Haartz, which makes automobile convertible tops and other products, confirmed the injuries in a message posted to Twitter around 1:05 p.m.

On Wednesday evening, the company said four employees who had been taken to the hospital had been released and a fifth was “still receiving care.’’

At about 10:25 a.m., Acton firefighters received a call about an explosion at the company, Deputy Fire Chief Robert A. Vanderhoof said at a news conference Wednesday afternoon.

Vanderhoof said the explosion occurred in the back of the building on the first floor, where the company operates an assembly line for automobile parts. The fire traveled through the air duct system to the second floor where the extinguishing system activated. The source of the explosion is unknown, and OSHA officials are investigating.

“The extinguishing system did a lot of the work, thankfully,’’ said Vanderhoof. “We just had to deal with the smoke, the victims, and the heat.’’

Crews from Concord, Boxborough, and Maynard assisted Acton firefighters, said Vanderhoof.

At the time of the explosion, a man was working on a machine nearby and suffered burns to his hands and back, said Vanderhoof. He was taken to Massachusetts General Hospital.

Haartz employees were allowed to return to work later in the day. Vanderhoof thanked the company’s safety staff for helping firefighters quickly find the site of the explosion.

“This company deals with some chemicals, some that are volatile and flammable,’’ said Vanderhoof. “They had a safety plan that was executed well. I wanted to commend them for their help.’’

Haartz bills itself on its website as the “World’s #1 supplier of automotive topping fabrics with a wide range of constructions and designs’’ and a “Leading producer and innovator of interior trim materials including moldable skins and artificial leather.’’

In addition to its headquarters on Hayward Road, the company also has locations in Michigan, Germany, India, Japan, China, and Mexico, according to its website.

Travis Andersen can be reached at travis.andersen@globe.com. Follow him on Twitter @TAGlobe.