Witness says a male student was initially spotted by other students at the bottom of school pool at the start of 5th period PE class, and other students and teachers jumped in the pool to help assist the student.
SKY7 flew above the school's swimming pool while police looked at a corner of it near the deep end.
Students were placed on a temporary lockdown but will be released from school at the regular dismissal time, police said.
Police said the lockdown was implemented as a precaution when the medical emergency happened but did not release further information about the victim or the nature of the emergency.
The school kept other students inside of classrooms while the situation unfolded. They were dismissed around 3 p.m., at the time classes usually end every day.
Danville police are currently investigating the incident.
Bay City News contributed to this report.