Rescuers are searching for three swimmers who went missing after falling from one of the pools at the top of Shannon Falls Tuesday.

Mounties in Squamish received a call from the BC Ambulance Service shortly before noon about three people who were swimming in one of the pools at the top of the falls. According to people who were there at the time, the swimmers slipped and fell into another pool about 30 metres below.

Search and rescue crews, paramedics, firefighters, police and members of BC Parks remained at the scene into the afternoon.

"As of 6 p.m. tonight we have been unable to visually see anyone in the pool system, but the terrain is difficult, very dangerous, and the water flow is heavy which is complicating the search," Mounties said in a statement.

Landon James, incident commander with Squamish Search and Rescue, said crews have been searching the area by helicopter and on land, and that they'd reviewed aerial footage provided by some bystanders who had been flying a drone over the area.

"At present time we have a rope rescue team that is descending one of the slopes into one of the pools to have a look to see if there's some spots that they can't see very well," he said.

They used a helicopter to help rescuers reach the pools.

"It's a very strong current. It is not a place anyone should ever go close to. Even if there's a trail going right down to it, stay away," James advised.

"The rocks are slippery even 10 feet up. Just don't get into that river."

Crews started at the swimmers' last known location and have expanded from there.

Few details have been confirmed, but an air ambulance with a stretcher basket arrived at the scene a short time before 5 p.m.

The RCMP said search efforts will continue overnight and into Wednesday if necessary. All trails leading to the pool system at the top of Shannon Falls will be closed until the search is complete.

Authorities have contacted the families of the missing swimmers, but are not revealing any of their identities.

Recent warm weather has contributed to the volume of water pouring over the falls, and the level is considered quite high.

With files from CTV Vancouver's Penny Daflos