The White House petition Web site is flooded with formal petitions by Chinese citizens, some on serious issues and others as jokes. ((Screenshot from White House Petitions site))

The Chinese people would like President Obama to stop an oil refinery from being built in southern China, endorse sweet-flavored tofu and reopen an 18-year-old criminal probe of a poisoning case. And while he’s at it, if he wouldn’t mind mobilizing U.S. troops to liberate Hong Kong, as well as China as a whole, that’d be great, too.

In a strange and diplomatically awkward turn of events, Chinese citizens have flocked to the White House’s Web site over the past week to lodge formal petitions, many of them directed against their government. Some are deadly serious, others frivolous and funny. A few have a touch of both .

Some of the signatures — more than 170,000 total on the various petitions as of Thursday evening — were undoubtedly posted in jest, but many more, Chinese online users say, reflect a sincere sense of powerlessness among people frustrated with their leaders’ repressive style of governance.

Comments critical of the government are banned on Chinese Web forums. And although each provincial capital maintains a petitions office, and thousands of people travel to Beijing each year to report local officials’ wrongdoings to the top-ranked State Bureau for Letters and Visits, such petitioners are often intercepted by thugs hired by those same local officials. They are held at “black sites,” at times beaten, then hauled back to their home provinces — a practice that has been documented and is the subject of petitions by human rights groups.

So, as the link to the White House petition Web site went viral this week on weibo microblogs — the Chinese equivalent of Twitter — some of that pent-up frustration found sudden release.

The case that jump-started the fad was an unsolved attack almost two decades ago on a college student named Zhu Ling. In 1995, Zhu was left severely disabled after a suspected thallium poisoning. Her roommate, Sun Wei, who had access to thallium at the university, was a suspect in the case. But she also happened to be the granddaughter of a high-ranking official thought to have close ties to then-President Jiang Zemin. No charges were ever filed, and Sun disappeared.

Talk of the long-dormant incident resurfaced last month after another student was poisoned in an unrelated case. Comments turned bitter as bloggers recalled Sun, citing her as an example of a rich, well-connected elite — the target of much resentment these days — that can get away with anything, even violent crime.

The government began censoring Zhu’s name online, and someone filed a White House petition demanding that Sun be deported from the United States, where many Chinese bloggers believe she lives. Soon after that, residents in the southern city of Kunming, blocked from organizing online opposition to a chemical plant, adopted the tactic. Others urged commemoration of those killed during the 1989 Tiananmen Square student protests, one of China’s most heavily censored topics.

But it didn’t take long for the petitioning — like all good Internet fads — to devolve into the absurd.

On Thursday, as some petitioners pushed for a U.S. ban on Beijing fried pancakes, other bloggers tweeted worries that the White House might start filtering their complaints, as China’s government has done for so long, despite the Web site’s familiarity with frivolous complaints.

“It’s because Chinese people have had to hold their voices for so long,” explained one blogger almost apologetically. The man, who spoke on the condition of anonymity because his account was suspended by censors on Wednesday, had renamed his microblog “Obama, director of China’s petition office” a day earlier in support of the campaign. “If only we had more opportunities to express ourselves, we would gradually be more and more mature.”

White House officials say the number of petitions from China represents a very small proportion of the more than 200,000 petitions that have been filed so far. There are no signs that the Chinese government is limiting access inside China to the Web site.

The White House promises a response to any petition garnering more than 100,000 signatures within 30 days — a number that the petition in the Zhu case has far surpassed. But how to do that diplomatically may prove tricky. State Department officials did not respond to calls for comment.

But at least in China, the online rally on behalf of Zhu has elicited a response from the government.

Authorities recently stopped censoring the name Zhu Ling, and on Wednesday, Beijing officials released an unusual statement defending their investigation of her case. Investigators weren’t trying to hide anything 18 years ago, they explained; they simply couldn’t identify the poisoner despite their best efforts.

Li Qi in Beijing and Scott Wilson in Washington contributed to this report.