The streets of Tokyo may be free of prowling dogs since its zero-stray policy came into effect but the laws come at a heavy price as one politician has revealed.

Ayaka Shiomura, a lawmaker in the Tokyo Metropolitan Assembly, recently went to visit an euthanasia centre in Japan and shown that the 'dream box' used to euthanise the country's strays are anything but humane.

The excruciating procedure involves putting strays into a gas chamber where they are slowly suffocated with carbon dioxide and the whole process can last as long as 15 minutes, reported People's Daily Online.

Locked up: Politician Ayaka Shiomura photographed the last moments of dogs in a Japanese euthanasia centre

Gruesome: The dogs die a slow and painful death after being gassed with carbon dioxide in a 'dream box'

Campaign: Ayaka Shiomura (pictured) hopes to highlight the issues surrounding Japan's stray dog policy

Ayaka Shiomura went to visit an unnamed facility, thought to be in Tokyo where the lawmaker is based, and posted about her experience on her website last month.

Euthanasia facilities like it are part of a zero-stray policy, which stipulates that all unclaimed cats and dogs must be euthanised in a set period of time according to Rocket News 24.

Shiomura explained in her introduction that any animals brought to the facility remains at the shelter for anywhere between three to seven days, depending on local policy.

After that time, if the animal is unclaimed, it will be disposed of.

During Shiomura's visit, 10 dogs were to be euthanised. Of those, some were thought to be pets as they still had collars on.

Automated: The dogs are kept in a case, which opens up at the back (pictured) straight into the gas chamber

Torture: Dogs howl in desperation as they slowly suffocate in the increasingly toxic levels of carbon dioxide

Cruel: The gas drives the oxygen from the dogs' system, effectively suffocating them as they wait helplessly

Death: Eventually, the dogs will die but the gassing continues for at least 15 minutes to make death a certainty

The dogs were kept in a cage, which has a back door leading straight into the 'dream box' - a romantic name that had little to do with the stark reality of the gas chamber.

The staff at the facility never have to touch the animals as they generally wander in on their own accord.

Once inside, the chamber is locked down and a button is pressed to disperse carbon dioxide into the chamber.

Elisa Allen, Associate Director at PETA, told MailOnline: 'Death by carbon dioxide or carbon monoxide can be extremely distressing and painful.

'Cats often slam themselves against their cages, desperately trying to escape. Dogs howl, cry and claw at the metal walls of the chambers while they're slowly poisoned.'

The cramped gas chamber is equipped with a glass window, which allows the operator to check the procedure is complete.

Disposal: After the dogs die, their collar are removed before they're thrown into the incinerator for disposal

Significant: Around 170,000 dogs are 'euthanised' in this way each year in Japan to cull its cities' stray animals

Through this window, Shiomura captured the final moments of the dogs' gruesome death through suffocation.

Shiomura described that the dogs were 'trembling' before the procedure but this soon became 'panting' and eventually 'collapsing'.

The chamber is gassed for 15 minutes to ensure the dogs are completely dead.

Finally, their remains are dumped into an incinerator to be disposed of.

According to news site TouTiao, Shiomura debated over whether to publish the post but felt that she needed to highlight the issue of animal culling.

She explained that in Japan, there's around 170,000 stray dogs and cats that are euthanised in this way but the procedure is far from kind.

Shiomura hopes that more people in Japan would consider the consequences of buying a pet before making the purchase.

There is hope: This dog and others like it have just a few days, where someone could claim them, before they die

There are more humane ways to euthanise animals.

Elisa Allen informed MailOnline: 'Animal shelters around the world condemn the use of such gases, choosing instead euthanasia ('mercy killing') by intravenous injection of sodium pentobarbital in the case of dogs, cats and animals of similar size, sometimes using other humane methods for smaller or larger animals.