Melbourne, Oct 1 China knew about the contamination of milk products months ago but covered the scandal up to prevent it tarnishing the Beijing Olympics, according to journalists, rights groups and media critics.

The crisis broke in mid-September, a month after the Olympics, but several Chinese reporters had long known about babies being hospitalised after drinking tainted milk, yet were muzzled by the authorities, news.com.au quoted critics, as saying.

An editor at a respected southern China newspaper said that as early as July one of his reporters was investigating how milk powder might have been to blame for children developing kidney stones and falling seriously sick.

"As a news editor, I was deeply concerned because I sensed that this was going to be a huge public health disaster," Southern Weekend news editor Fu Jianfeng said on his blog.

"But I could not send any reporters out to investigate. Therefore, I harboured a deep sense of guilt and defeat at the time."

Fu's blog posting was later removed, although it could be read on some overseas Chinese websites.

An estimated 53,000 Chinese children have been sickened after the industrial chemical melamine was added to milk products, and four infants have died.

The first of the baby deaths was on May 1, more than four months before the scandal went public.

Starting with Sanlu milk powder, the scare has gone on to envelop numerous Chinese firms and international companies operating in China, including global giants Cadbury and Unilever.

Chinese premier Wen Jiabao vowed over the weekend to work to restore his country's reputation, saying it was facing the problem "candidly".

However, there are claims that Chinese authorities reverted to the familiar practice of squashing the negative news reports, apparently conscious of the damage it would do to the Olympics.

Sanlu Group began receiving complaints of sick children as early as last December, a recent cabinet probe found in an apparent attempt to shift the blame for the delay.

It also said Communist officials in the northern city of Shijiazhuang, where Sanlu is based, delayed referring the matter to higher authorities for more than a month after Sanlu finally told them of the problem on August 2, six days before the Beijing Games began. (ANI)