Alsina, 22, is receiving treatment for multiple seizures at an unnamed hospital, TMZ reports. The "No Love" singer fainted during his stage show - which was captured in a video obtained by the gossip site.
Doctors believe Alsina may have collapsed due to "exhaustion and dehydration," TMZ reports, adding that no alcohol or drugs - apart from marijuana - were found in Alsina's system.
Witnesses said Alsina was walking near the front of the stage during the Irving Plaza gig when he suddenly fainted. He appeared to be "out cold," according to the initial reports.
Alsina was rushed to the hospital after being carried backstage by several of his security guards. Paramedics were called to the scene.
The "Numb" singer's concert in Cincinnati on Tuesday was quickly postponed after it was revealed he remains hospitalized. His show scheduled for Friday in Indianapolis remains uncertain, according to MTV News.