The 21-year-old singer on Thursday had just performed her single, "Boyfriend" for MTV Japan, when she told the audience she felt sick and said to them, "I love you guys," Us Weekly reported Friday. She then collapsed in an elevator and was rushed by ambulance to a hospital.
Her representative, Rob Shuter, confirmed the report to The Associated Press, but would not give further details or provide Simpson's condition.
Simpson, the younger sister of Jessica Simpson, has been touring to support her sophomore album, "I Am Me." She infamously was caught lip-synching her "Saturday Night Live" performance in October 2004.
Her upcoming appearance at the Radio Music Awards on Monday has been canceled.