Legal authorities in China ordered lawyers not to take on cases from the families of victims of last weekend's fatal train crash, it emerged Saturday, as judicial officials apologised for the move.

Three days after the crash near Wenzhou in eastern China, law firms in the city received an "urgent statement" in the names of the Wenzhou Judicial Bureau and the Wenzhou Lawyers' Association, the official Xinhua news agency said Saturday.

The statement said lawyers should report to the two organisations "immediately after the injured passengers and families of the deceased in the accident come for legal help," the agency reported.

Xinhua said the statement also told lawyers not to "unauthorisedly respond and handle the cases," because "the accident is a major sensitive issue concerning social stability".

Forty people were killed when two high-speed trains collided last Saturday on the outskirts of Wenzhou, the worst accident yet to hit China's rapidly expanding high-speed network, now the biggest in the world only four years after it opened.

The accident has raised questions over whether safety concerns may have been overlooked in the rush to expand the network, and China's state-controlled media has been unusually outspoken in its coverage of the accident, defying directives not to question the official line.

There has been widespread criticism of the government's handling of the accident and its aftermath in Chinese media and online, and the instructions to lawyers prompted an angry response when they were publicised by web users.

"The judicial authorities and the lawyers' association in Wenzhou have banned lawyers from taking victims' cases. Who are they working for? I'm having doubts about the independence of Chinese justice," wrote one web user, Dianfuzishangwudeguairen, on the Sina microblog service.

The Wenzhou Judicial Bureau apologised for the statement, which it said the lawyers' group had issued without its approval.

"We didn't know the content of the statement before it was released. It was written by the lawyers' association, which used our name without authorisation," Liu Xianping, director of the bureau's office, said in remarks quoted by Xinhua.

A Wenzhou Lawyers' Association spokesman confirmed this version of events, Xinhua said, adding that they issued the order because they feared "conflicts would be generated if legal services are not well-provided".

Chinese Premier Wen Jiabao has ordered an "open and transparent" probe into the crash and said those responsible would be "severely punished".

Rail officials have admitted the Chinese-made signalling system was to blame and the company that built it has apologised.

Amateur video posted online has shown bulldozers pushing the wreckage of carriages into a ditch. On other clips, web-users say they can see one or two corpses falling to the ground at the same time as a carriage left hanging at the crash site is deliberately toppled over.

On Friday evening the railways ministry said that the carriages had to be pushed off the viaduct for rescue operation purposes, and no evidence had been lost as a result.

But the footage has done nothing to ease criticism, particularly as a two-year-old girl was found alive in the wreckage 21 hours after the accident, long after rescue operations had been declared over.

Wen's own trip to the site five days after the crash raised further questions, when he said that his visit had been delayed because he had been in bed sick for more than a week -- a highly unusual admission in China, where the health of top leaders is considered a state secret.

Photographs on the central government website of Wen meeting a Japanese delegation the day after the crash appeared to contradict his claim, and analysts suggest leaders may have disagreed over how to handle the disaster.