Most of the pilot whales that were stranded in the Florida Everglades swam into deeper water on Thursday while rescuers tried to chase the rest out to sea by banging on pipes and revving their boat engines.

Wildlife workers had hoped the cacophony would encourage the whales to leave the shallow water where dozens of short-finned pilot whales were first sighted on Tuesday afternoon in a remote part of the Everglades National Park.

The National Oceanic and Atmospheric Administration, or NOAA, said via Twitter that of the 51 whales originally stranded, 11 had died and five went missing overnight on Wednesday.

NOAA said the 35 swimming away were about 14 kilometres from shore, in about five metres of water, with about 16km or 25km to go before they reach deeper waters.

Biologists were collecting samples from some of the carcasses in hopes of learning how they died. There were also sharks in the area, feeding on the carcasses of the dead whales, NOAA said.

Biologists said that beached pilot whales often re-beach and that survival rates in mass strandings were very low.

About three dozen would-be rescuers from NOAA, the National Park Service, the Florida Fish and Wildlife Conservation Commission and police set out in boats for the rescue effort, while the Coast Guard tracked them from the air.

A Coast Guard cutter crew was also enforcing a safety zone to protect the whales and keep sightseers away.

Pilot whales live in tightly cohesive groups and typically will not leave ailing or dead members behind. They are a deep-water species that forages on squid, octopus and fish and cannot live long in shallow water.