Hong Kong (CNN) When Ho Feng Shan died at the age of 96, he took a secret to his grave. The only clue was a single sentence in his obituary in 1997.

Throughout his long life, Ho never mentioned his heroic deeds during World War II — not to his wife, his children or friends.

During 1938 to 1940, Ho, the consul general of the then Nationalist Chinese government's consulate in Vienna, saved perhaps tens of thousands of Jews from the Holocaust with just a stroke of his pen.

When Jews desperately sought visas to escape from Nazi-occupied Austria, he issued thousands — in defiance of his superior's orders.

The exact number of entry papers Ho issued -- and the number of lives saved -- may never be known, as too many have already been lost to time.



But based on the serial number of one visa nearing 4,000, the best estimate is that thousands of visas were issued.

China's Schindler?

Ho is often hailed as "the Chinese Schindler," in honor of the industrialist Oskar Schindler who saved 1,200 Jews by employing them in his factory located in Poland.

"Nowadays most people believe that he saved more than 5,000 lives at the time," said Xu Xin, a professor and a leading expert on Jewish studies at Nanjing University.

"More importantly, Ho was probably the first diplomat to really take action to save the Jews."

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While other countries refused to issue visas in fear of aggravating the Nazi government, Ho threw his weight behind the Jews.

And when the Nazis confiscated the premises that housed the embassy because it was owned by a Jew, Ho opened a new office with his own money to continue the rescue.

"It was totally in character," says Manli Ho, daughter of the late diplomat, who has been researching her father's story for some ten years.

"That is the kind of person he was -- very principled, straightforward, and has integrity."

How the visas worked

The visas Ho gave out were unique-- they were only for Shanghai, an open port city without any immigration controls and occupied by the Japanese army. As a result, anyone could enter without a visa.

So why did he issue visas to a place that doesn't require one in the first place? Here's where Ho's sophistication shines through.

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The holders of Ho's visas didn't all travel to Shanghai but they were able to use the papers to get a transit visa and escape elsewhere -- the United States, Palestine, and the Philippines to name a few destinations.

But the fact that Ho kept issuing Shanghai visas created a buzz among the Jewish community and the city earned its own reputation as a safe haven.

"It's like gossip. All of a sudden the Jews heard about Shanghai visas, and they were desperate to escape. So the name Shanghai spread very fast like wild fire, and also the fact that Shanghai did not need any kind of document," said Manli.

A Shanghai visa signed by Dr. Ho Feng Shan with a serial number of 3639.

A survivor's tale

Among those who received a visa was Eric Goldstaub, who was 17 years old when he received one of 20 Shanghai visas issued for his family.

When the Nazis annexed Austria, he started knocking on consulate doors in search of visas to leave, only to be turned down time after time. After 50 attempts, he stumbled upon the Chinese consulate, where Ho extended his welcome.

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"What a surprise waited for me! A nice reception, a friendly smile and the following message: Bring your passports and we will give you the visas for our country," wrote Goldstaub in his memoir.

Goldstaub passed away in 2012 at 91 years old in Toronto, Canada. He was survived by two sons and a daughter.

"He was very active; he liked soccer, snow skiing. Even in his nineties he swam every morning and walked every day," Danny Goldstaub, his son said.

The significance of the Shanghai visa hasn't escaped his descendants.

"I mean -- if you look at the family tree, without Dr. Ho, a lot of lives would not be existing right now," said the younger Goldstaub. "He saved a lot of lives at that stage."

The Shanghai Jewish settlement

Amid the ravages of the war, Japanese-occupied Shanghai became a "Noah's Ark" that sheltered around 25,000 Jewish refugees fleeing the Nazis.

In 1943, the Japanese occupiers cordoned off an area called the Restricted Sector for Stateless Refugees -- more commonly known as the Jewish Ghetto -- and made the Jews move in.

Life was tough inside the ghetto, says Wang Jian, a history professor researching modern Jews in China at the Shanghai Academy of Social Sciences.

Residents had to live in crowded, unsanitary rooms and face the threat of persecution by the Japanese military.

Despite the challenges, the Jewish refugees established businesses and managed to thrive.

The settlement soon took on the appearance of a German or Austrian city; a road was called "Little Vienna" for its cafes, shops and nightclubs.

Theater groups and an orchestra were formed, sports teams -- from soccer to table tennis -- sprang up, and over ten German publications produced by editors and journalists among the refugees were circulated.

Today, only a handful of remnants stand as testimony to this history although organizations like the Shanghai Jewish Refugees Museum are trying to change this.

Conscience and compassion

A photo of Manli Ho (L) and Dr. Ho Feng Shan (R) in 1977.

Ho was an unassuming man who grew up poor and fatherless in China, and rose to become a diplomat. Since Ho seldom spoke of the events in Vienna, the public knew little of his involvement while he was alive.

His story came to light by accident, when his daughter -- a reporter at the time -- wrote his obituary, in which she included a tale of him confronting the Gestapo at gunpoint to save his Jewish friends -- the only wartime tale he ever told her.

A curator of an exhibition about diplomat rescuers picked up the obituary and contacted Manli. This made her curious and prompted her to retrace her father's footsteps.

On April 21, 2015, a plaque was unveiled at the site of the former Nationalist Chinese embassy in Vienna to commemorate Ho's actions.

Ho spent the rest of his life in San Francisco, California. It wasn't until long after his death that the diplomat received recognition for his courage in saving thousands of Jews from the Holocaust.

In 2000, Israel posthumously bestowed the title of "Righteous Among the Nations," one of its highest civil honors.

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He is one of the only two Chinese to be conferred that status. The other is Pan Yun-shun, who received the title in 1995, after sheltering a Jewish girl during the occupation of part of the Soviet Union.

The U.S. Senate passed a resolution honoring Ho's heroic deeds in 2008. And earlier this year, a commemorative plaque was placed on the former Chinese Consulate building in Vienna, which is now a Ritz Carlton Hotel.

In Taiwan, where the Nationalist government fled at the end of World War II, he will be honored by President Ma Ying-jeou as p art of a series of events this summer to mark the 70th anniversary of the end of the war in Asia.

In his Chinese-language memoir published in 1990, Ho described how he was deeply moved by the Jews' plight:

"Seeing the Jews so doomed, it was only natural to feel deep compassion, and from a humanitarian standpoint, to be impelled to help them."

But we'll never know why he chose to keep his heroic acts a secret.

"If you have been given a lot, you have to give back. That's his ethics, and he basically lived it," Manli, his daughter says.