Jin found himself at the bank branch just after midnight to withdraw 95,000 yuan for his friend from a village 20 kms (12 miles) away.
"He was uncomfortable. It was late and he couldn't wait, so he left me his ID card to withdraw his cash," Jin said.
By Tuesday, the crisis of confidence had engulfed another bank, the nearby Rural Commercial Bank of Huanghai.
"One person passed on the news to 10 people, 10 people passed it to 100, and that turned into something pretty terrifying," said Miao Dongmei, a customer of the Sheyang bank who owns an infant supply store across the street from the first branch to be hit by the run.
Claiming to be a Yancheng resident, one user of Sina Weibo's Twitter-like service repeated the story on Monday about the failed 200,000 yuan withdrawal, adding that "rumours are the bank is going bankrupt."
When later contacted by Reuters online, he said he had heard the rumour from his mother when she came back from town.
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Huanghai and Jiangsu Sheyang banks declined to comment. Yancheng police said on the force's official microblog on Thursday that they had detained a person suspected of spreading rumours.
China's banks are tightly controlled by the state and bank bankruptcies are virtually unheard of, so the crisis has baffled many outsiders.
Yet in Sheyang, fears of a bank collapse resonate.
In recent years, this corner of hard-strapped Jiangsu province has experienced a boom in the number of loan guarantee, or 'danbao', companies and rural capital co-operatives.
These often shadowy private financial institutions promised higher returns on deposits than banks, but many have since failed.
Qu Guohua, a spiky haired former migrant worker in his 50s, nearly lost 30,000 yuan in a credit guarantee scheme that went up in flames.
What saved him one day in January 2013 was a tip-off from a friend at a rural co-operative just down the street from the loan guarantee company where he had his money.
"He told me the other one was going to go out of business and I better go get my money quick," he said.
Qu managed to get his cash, but others behind him in line were not so lucky, he said.
That helps explain why lines formed so quickly once the rumours started circulating this week. Luck has it, he deposited the cash in a bank next door: Sheyang Rural Commercial Bank.
Banks are different than credit co-operatives and guarantee companies in that they are regulated by China's banking watchdog and subject to strict capital requirements.
On Wednesday, officials' painstaking efforts to drive that message home were in full swing.
Bank managers stacked piles of yuan behind teller windows in full sight of customers to try to reassure them that they had plenty of cash on hand. Local officials used leaflets, radio and television to try to calm nerves.
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Near one of the troubled banks, a branch of the China Construction Bank - one of China's 'Big Four' state-owned banks - was running a ticker message on an electronic board over the entrance stating: "Sheyang Rural Commercial Bank is a legal financial organisation approved by the state, just like us".
While small groups of depositors still gathered at several bank branches in and around this part of Yancheng, some arriving by motorbike, others by three-wheeled motor vehicles common in the Chinese countryside, there were signs that the banks' efforts were bearing fruit.
Jin said he did not panic when the rumours were spreading and on Wednesday, like many others, he made a deposit.
Others, like Qu, are holding their nerve.
On a visit to see his hospitalised granddaughter, he decided to nip into a local bank where he still has about 10,000 yuan - just for a look.
"I'm not nervous about my money in the bank. It's protected by national law."