It happened around 5:40 a.m. at the A Line's Allen Station.
Details are limited, but according to a statement from Metro, LASD deputies "swiftly apprehended" the suspect after the incident. The woman was sent to a hospital in stable condition.
"Metro wishes the woman a speedy and full recovery," read the Metro statement.
The incident remains under investigation.
Leaders speak out
Los Angeles County Supervisor and Chair of the Metro Board of Directors Janice Hahn issued a statement Wednesday afternoon, calling the incident "disturbing."
"I am grateful that the victim is recovering and that the suspect is in custody," she wrote. "Our board will need a full investigation into this incident, an accounting of where both Metro's contracted law enforcement and transit security were when this woman was attacked, and a plan to increase security during early morning commuting hours. Our trains, buses, and stations must be safe for our riders and we have to continue to implement safety reforms to get our system to that point."
Los Angeles County Supervisor Kathryn Barger also issued a statement, saying she's "outraged" to hear of another attack on the Metro system.
"I want to commend the transit deputies who responded quickly and apprehended the suspect.
This incident is a perfect example of why we need to urgently address safety issues, not only on the Metro train system, but also at stations. I expect a full report from Metro on what security measures will be put in place to increase security, especially during early morning commute hours.
Our Metro Board has already taken some steps to improve public safety, including enforcing fares. But, it's obvious to me that our Metro system commuters are still confronted with serious safety issues that cannot be ignored."