Beluga whales, like this one, as well as killer whales were held in a so-called "whale jail"

Whales captured to perform in aquariums and held in cramped pens in far eastern Russia on Friday were journeying in trucks back to their home waters after President Vladimir Putin backed their release.

The first batch of eight killer and from the total of nearly 100 held in a so-called "whale jail" were being trucked north before taking river boats to the Sea of Okhotsk, where they had originally been caught, officials said.

Putin during his annual phone-in with ordinary Russians on Thursday said "thank God things have started moving" on the whales after their fate evoked expressions of horror from animal welfare groups.

The whales belong to commercial companies that caught them for "cultural and educational purposes" under a legal loophole Russia has now said it will close.

They are being kept in waters off the port city of Nakhodka and had been destined for aquariums in China where this industry is booming.

The firms that own the whales have been fined by courts.

Russian television showed footage of whales being hoisted in slings into tanks of water and transported in huge, slow-moving trucks.

"The mammals were loaded successfully and we are counting on them being delivered safe and well," the head of the All-Russian Fisheries and Oceanography Institute leading the operation, Kirill Kolonchin, said in a statement.

Putin backed the release of whales, which were held in cramped pens and intended for commercial aquariums

The whales on Friday had covered more than 600 kilometres (400 miles) to reach the far eastern city of Khabarovsk on the Amur River, one of the region's main waterways, the institute said.

Monitored by scientists and vets, the whales will then take a boat trip up the Amur and be released on the shore of the Sea of Okhotsk.

The first whales are set to be released Monday, a regional official told RIA Novosti state news agency.

The whole process of releasing all the could take four months, officials have said.