Emergency services were called to the complex on Rockvale Road in Armidale, northern NSW, about 2.15am on Thursday.
A woman believed to be aged in her 40s was found inside the home with multiple stab wounds, police said.
She died at the scene, despite paramedics' efforts to save her.
Vincent Raymond Blair, 53, was arrested and later charged with murder.
Inspector Greg Ryan said police were treating the incident as domestic violence murder and both parties were known to authorities.
The victim's family was devastated, and first responders faced a confronting scene in the unit, he said.
"These scenes are obviously quite tragic for emergency services to attend, as you can imagine, based on the circumstances, what that would be like," he told reporters on Thursday.
"It's not a nice job to go to."
Officers seized a knife at the unit, Insp Ryan said.
He extended police support to the wider community, saying a "big part" of local officers' jobs was domestic violence responses.
"Please come forward if you have concerns in relation to it ... our focus is to respond to domestic violence and protect victims," he said.
Domestic Violence NSW chief executive Delia Donovan told AAP women in regional areas faced unique barriers to safety.
Housing shortages, long distances, limited transport, workforce shortages and inadequate justice infrastructure pose additional risks, she said.
She welcomed government funding contributions but said, in the state's regions, availability did not necessarily mean accessibility.
"We need funding models that reflect the true cost of delivering specialist DFV services in regional and remote areas, enabling services to recruit and retain staff, cover vast geographical areas and provide timely, specialist support," she said.
"This requires greater investment in services, housing and the specialist workforce, alongside place-based, locally led responses."
Blair did not appear in a bail court on Thursday as his lawyer made no application for his release.
He will next appear at an Armidale court via video link on December 16.
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