A 21-year-old Mexican man is in a coma and eight others were hospitalised after party organisers poured barrels of liquid nitrogen into a pool.
Partygoers filmed the moment four large buckets of the liquid were tipped into a pool, sending toxic plumes of smoke into the air and leaving guests gasping for breath.
The extremely cold liquid became toxic when mixed with the chlorine in the outdoor pool, causing swimmers to pass out.
Victims were pulled to safety by paramedics but one man, Jose Ignacio Lopez del Toro, remains comatose, Univision Noticias reports.
The eight others hospitalised have since been released but some were diagnosed with cardiovascular problems.
Around 200 young guests had been invited to the event in the city of León hosted by German liquor brand Jagermeister.
Nitrogen in its liquid form is extremely cold and can be very dangerous.
Author: Nick Pearson. Approving editor: Matthew Henry.