By Michael Battye

BEIJING (Reuters) - Hong Kong reported its highest one-day jump in SARS deaths on Saturday as China intensified its newly open war on the virus by threatening to punish officials caught covering up cases.

Hong Kong said 12 more people had died, taking its toll to a world-leading 81, just a day after the territory' leader, Tung Chee-hwa, said the outbreak would "stabilize gradually."

It has now had 1,358 cases of Severe Acute Respiratory Syndrome, almost as many as on the Chinese mainland where the deadly virus first appeared in the southern province of Guangdong, the former British colony's neighbor.

Hong Kong was the first place SARS erupted outside the mainland and Singapore was not far behind as air travelers carried SARS around the world to infect people in 25 countries.

Singapore said on Saturday it may be facing the worst crisis since independence as SARS threatens to wreak havoc on its economy.

Singapore Prime Minister Goh Chok Tong said his island nation was having some success in limiting infection rates, but more needed to be done to tackle the climate of fear causing damage to the vital tourism and transport industries.

"If we fail to contain SARS in Singapore, it may become the worst crisis that our country has faced," Goh told a news conference. "The economic costs are huge."

That cost could top $850 million, he said.

CHINA GETS SERIOUS

The threat of punishment from Premier Wen Jiabao was another sign China, accused of telling the world too little, too late about the outbreak of a new disease with no known cure, was getting serious about SARS.

Newspapers, all supervised by the Communist Party or the government, gave prominent coverage on Saturday to Wen's threats and his demand that officials at all levels come clean on SARS.

"Anyone who covers up SARS cases or delays the release of information will be harshly punished as this matter concerns the people's health and safety," the English-language China Daily quoted Wen as saying during a tour of schools on Friday.

That came shortly after the nine-man Communist Party Politburo Standing Committee, whose word is law, ordered an all-out war against SARS and full disclosure of the impact of a bug which has killed 172 people and infected nearly 3,500 around the world.

The disease, which is fatal in about four percent of cases and has no known cure, has also dealt a mighty blow to Hong Kong.

On Saturday, hundreds of thousands of its people fought back as folks from housewives to government officials armed with brooms and mops launched a city-wide clean-up campaign to battle the virus.

"Overall, the situation will stabilize gradually," chief executive Tung said on Friday.

The disease has spread as far as Canada -- where the only known deaths from it outside Asia have occurred -- and other countries are taking tough action to keep it out.

A group of British boarding schools quarantined dozens of children arriving back from Asia for the new term, whisking them straight off for 10 days of isolation.

Vietnam's health authority has proposed the country's border with China be closed temporarily to prevent the bug from crossing the frontier. The proposal was awaiting a government decision, officials said.

CHINA'S NUMBERS TO RISE

China's SARS numbers, at least of victims, are expected to rise after Beijing promised to revise its figures following charges -- some of them from within party ranks -- that the city was not telling the truth about how many people had caught it.

The World Health Organization said the Beijing government would raise its toll "significantly" after agreeing to alter the way it defines patients with symptoms of the flu-like virus.

"Their expectation is that the number will be significantly greater than what is officially reported," James Maguire, head of the WHO expert team, told Reuters on Friday.

"The people at the top are totally on board," he said. "What we're seeing now is movement toward an urgent response and really putting resources behind it."

The experts said they suspected Beijing had between 100 and 200 cases but was reporting only 37, possibly because of differing definitions of what constituted a confirmed case.

There are fears SARS, which has cropped up in places as remote as Ningxia in the far west, may spread further around China when about 100 million people travel during a week-long holiday in early May.

Many of those will be migrant workers going home for the May Day holiday, but the government is trying to discourage people from venturing far.