A giant squid that wandered into a Japanese port has been guided back out to sea almost a week after it was spotted, giving enthusiasts and experts a rare glimpse of the mysterious creature.

The massive invertebrate, four metres (13 feet) in length, was discovered by fishermen on December 24 at a port in the city of Toyama on Japan's northwestern coast.

It was later guided by a diver into deeper seas.

"Its suckers were so strong that I felt some pain," Akinobu Kimura, who runs a dive shop in Toyama, said on TV Asahi.

"Even though I was trying to let it escape (from the port), it wrapped around my body and clung to my arm."
A curator at the local Uozu Aquarium who visited the port and took underwater photos of the squid was surprised at its size.

"It was unexpectedly beautiful, its body glowing red," he said in footage shown on broadcaster TBS.

Giant squids are sometimes caught in Japanese fishing nets, though filming a live one is rare.

The giant squid, "Architeuthis" to scientists, is sometimes described as one of the last mysteries of the ocean, being part of a world so hostile to humans that it has been little explored.