Police in York Region are probing the sudden death of a 21-year-old woman at an after-hours club in Markham.

The woman, who turned 21 on June 4, was found unconscious and not breathing at the back of Club Rio at around 4:30 a.m. Sunday. Police say drugs may have been a factor in the girl's death.

Though police are not publicly releasing her name, they say the woman is Asian and she was visiting Ontario from Surrey B.C. She travelled here with her parents, Det. Const. Jim Woodcock told CTV.ca.

Her parents, who were travelling in Montreal this weekend, have been notified.

"We're just waiting to meet with them" he said. "They were inconsolable."

For now investigators are trying to determine who accompanied the woman to the club. Though she was seen with two Asian men in the hours before she died, police think she may have gone to the club with another woman.

However, when security guards inside the venue found the woman, her companions had vanished.

"They just left her there," Woodcock said. "They just left her there to die."

The woman was rushed to Markham-Stoufville Hospital where she was pronounced dead. An autopsy on her body confirmed to police that the woman did not die of a physical injury. Toxicology tests are now being conducted.

Investigators have a list of about 300 people who attended the Woodbine Avenue hot spot. They are looking to speak to anyone who may have seen the woman inside Club Rio.

Woodcock said the club owners and security guards have been cooperating with police and have handed over surveillance video.

Club Rio is an all-ages club that is open from 11 p.m. until 7 a.m. Woodcock said the club used to be known as Viva Nightclub, a spot where police were routinely called to break up fights and arrest people for drugs.

Police even investigated a homicide there but ever since the club was taken over by new owners, authorities have not had much trouble with the venue, Woodcock said.

"Right now we're pleading with the people that were with her to come forward and talk to us," he said.

Anyone with information can call investigators at 905-881-1221 ext.7541.