"We have to seek justice, understand what happened and find who is to blame. Otherwise we will have let down this group of departed spirits who have not yet been laid to rest."
The Shanghai health authority did not respond to questions by telephone or fax.
Several dozen relatives banded together on Sunday to go to government offices to get information, three members of the group said. But they got no answers.
"We just couldn't bear this any more," said Gu Yinjuan, the elder sister of one of the dead who joined the group.
"All along they haven't told us anything, we've just been waiting and waiting."
Relatives also said attempts to tell their stories were being blocked. A microblog relatives set up to share information was shut down on Monday, one said.
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Another relative said domestic media outlets, many of which are state-run, were ignoring their plight while trying to put a positive spin on the accident.
"Domestic media reports are very proper, shrouding the truth so it doesn't come out," said the relative.
People who said they were police but did not identify themselves contacted several Reuters staff by telephone to warn against "being used" by relatives.
There have been critical reports in domestic media, including questions about the number of police on duty and their apparent inability to control the crowd.
"It was a lack of vigilance from the government, a sloppiness," the official Xinhua news agency said.
Waterfront fireworks that attracted more than 300,000 people the previous year had been canceled but huge numbers still came. One police officer who declined to be identified said they had not expected such a big crowd and had been under-staffed.
Most victims were in their twenties, with 25 of them female, according to a police list.
President Xi Jinping has urged the Shanghai government to get to the bottom of the city's worst accident since 58 people were killed in an apartment building fire in 2010.