Police are investigating after a woman died inside an apartment building in Vancouver's Mount Pleasant neighbourhood early Monday.

Officers were called to the building near Ontario Street and First Avenue for a "disturbance" around 2:30 a.m., according to a statement. Police arrived to find a woman who'd been fatally stabbed.

The 51-year-old woman died at the scene.

A man, also 51, has since been arrested.

"Investigators believe the suspect and victim knew each other," police said.

The man was not identified because he has not been charged. Police said the investigation into the woman's death, which is the city's third homicide of the year, is ongoing.