A California mother suspected of killing her infant daughter threw her toddler son off a second-story balcony before jumping herself -- and landing on her face, police said.

Tierra Ortega, 24, is expected to be booked on charges of suspicion of homicide, attempted homicide and child abuse resulting in death following the incident at her Upland apartment Tuesday night, police said.

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"This is very unusual. It's extremely tragic," Upland police Capt. Marcelo Blanco said.

Upland police officers went to the apartment building after a neighbor called 911 to report a screaming child. The caller then reported seeing Ortega holding the 1-year-old boy over the second story landing and dropping him. Tierra proceeded to jump off the balcony as cops arrived.

"From what we gather, it was an intentional act, it wasn't accidental,” Blanco said.

Ortega and her son were given first aid at the scene. Officers then entered her apartment, where they said the 24-year-old’s daughter, believed to be 6 to 7 months old, was found unresponsive and not breathing.

Ortega and her children were taken to the hospital where the baby girl later died of her injuries. Blanco said officials believe the child had a skull fracture and some internal injuries, though it’s unclear how she was hurt.

The 1-year-old boy suffered a broken foot from the fall. Ortega was treated for facial injuries.

Residents at the apartment building described the horrific scene to KTLA. Michelle Furlong said a neighbor was also taken to the hospital after she suffered a nervous breakdown from watching Ortega toss the toddler off the balcony.

"It really affected her. She said she seen the baby thrown, how she grabbed the baby and threw it and then she threw herself," Furlong said. "My heart is broken because they're two innocent kids.”

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It’s unclear what led up to the incidents. Ortega’s husband, who reportedly works in the waste management industry, was not home at the time and found out about what occurred when he saw police at his apartment, KTLA reported.

He spoke to police but "has no idea what led to this," Blanco said.

Police said an investigation is ongoing to determine the motive.