Dozens of police and SWAT officers surrounded a real estate company office in Valparaiso, Ind., on Friday after at least three gunshots were heard. A gunman inside the building was reported to be holding as many as 15 hostages, police and witnesses said.

The gunman allowed five people to leave the 21st Century real estate office, a witness told NBC News.

Few other details were available, but people who gathered in the parking lot as news of the situation spread told NBC News that they were receiving text messages from people inside the building, who relayed that the standoff was the result of a domestic dispute between the man and his girlfriend.

Police said the man entered the stand-alone building in Valparaiso, a southern suburb of Chicago, at 10:05 a.m. CT (11:05 a.m. ET). They said they hadn't yet identified the gunman and wouldn't comment on whether they've been able to make contact with him.