Cassius and Roxie have spent three months at a Hong Kong dog shelter waiting for new owners.

The two mongrels are victims of a surge in pet abandonments as the city experiences an exodus of residents due to China's crackdown on dissent as well as some of the world's strictest Covid restrictions.

They were brought to Hong Kong Dog Rescue (HKDR) after their owners made a sudden decision to relocate back to Britain.

It is an all too familiar story to people running animal shelters in Hong Kong these days.

"We are always full house," Eva Sit, communications director at HKDR, told AFP against a backdrop of near-constant excitable barks and yowls.

"We find it very difficult to say no to surrender requests because we feel very bad for the dogs."

Those giving up their pets, Sit explains, fill out a form that includes the reason why.

Emigration used to account for two in 10 cases.

"These days, it's almost the only reason. Like, maybe eight out of 10 surrender requests we get come with that reason," she said.

A huge number of local and foreign residents have quit Hong Kong over the last two years because of the political clampdown and harsh Covid control measures.

While much of the world, including rival Asian business hub Singapore, has switched to living with Covid and are reopening, Hong Kong continues to follow a lighter version of China's strict zero-Covid rules.

The result has been a sudden population decline.

Between 2020 and 2022, there was a net outflow of around 200,000 residents, according to government figures.

Normally, most of those leaving would take their pets with them.

But Hong Kong's self-imposed pandemic isolation has made that increasingly hard.

Once one of the world's busiest airports, Hong Kong International is handling just a fraction of flights compared with pre-pandemic levels.

Many airlines are avoiding the city entirely because of its mandatory quarantine rules.

In July, just 401,000 passengers went through the airport -- six percent of pre-pandemic levels.

The shortage of commercial flights means few available places for pets in the cargo hold or in the cabin, making emigrating with them either impossible or prohibitively expensive.

Wealthier residents have even clubbed together to rent private planes to get animals out, with slots going from anything from HK$150,000-HK$250,000 (US$19,000-US$32,500).

"It's very expensive, so I respect people who've done it," said Olivier, a French resident and dog owner, who has seen multiple friends plump for communal private jets.

But many others have to make the heartbreaking decision to leave their pets behind.

Narelle Pamuk, founder of Sai Kung Stray Friends (SKSF), said that owners are often left with no choice.

"They say people are bad when they leave their animals, but I have to say, not everybody is bad," she told AFP, adding that many simply could not find a flight -- or afford one.

"This whole pandemic has put people out of sorts completely. People didn't get a lot of warning, when they were losing their jobs, and they couldn't always take their pets with them because it's not easy."

Harvir Kaur, a 23-year-old teacher in Hong Kong who is emigrating to Canada next year, is factoring the needs of her three-year-old pomeranian, Taffy, into her travel plans.

Kaur is not comfortable with sending her dog by cargo, the sole pet transportation option provided by Cathay Pacific, Hong Kong's flagship carrier.

Instead, she is looking into options that allow her dog to travel in-cabin with her, regardless of costs.

"I've never thought of leaving Taffy behind, I think that would be unethical," she said.

"When you get a dog, it's not just a playtoy for you. Your dog needs you, maybe even more than you need your dog."