HONG KONG — China's days as the place to do cheap but dirty mining and manufacturing may not be over, but a growing environmental movement has made potentially polluting projects much harder to build and operate.

Large and sometimes violent demonstrations against the planned construction in southwestern China's Sichuan province of one of the world's largest copper smelting complexes prompted local officials to continue backpedaling furiously Wednesday.

The local government of Shifang, the planned site of the smelter, announced in a statement that the construction of the $1.6 billion complex had not just been suspended but permanently canceled.

The vast complex was supposed to be a centerpiece of the economic revitalization of an area devastated by the 2008 Sichuan earthquake, through the creation of thousands of construction jobs at a time when the overall Chinese economy is suffering a sharp slowdown.

A police official in Shifang said in a telephone interview that everyone detained in the protests had been released. Police acted after a crowd, estimated by local residents to be in the tens of thousands, had assembled Tuesday evening and demanded the release of dozens of students jailed in the protests Sunday and Monday, defying a police order Tuesday afternoon that any further protests would not be tolerated.

The success of the Shifang protests is only the latest in a series of large, sometimes violent demonstrations against projects that are perceived as heavily polluting. These protests have been coming with increasing frequency in the past year, raising questions about the viability of building projects in China without environmental safeguards.

"The standards for environmental protection are higher and higher, from the public and also from the government," said Zhao Zhangyuan, a retired environmental-protection official who has successfully campaigned for the past several years to block the construction of a large trash incinerator in a prosperous Beijing neighborhood.

Environmental protests, like the one in Shifang, seem to be accelerating in tempo and mark a new willingness by the Chinese people to challenge local authorities.

The financial penalties are increasing for Chinese companies and their owners that plan projects perceived as hazardous. Shares in the Sichuan Hongda Chemical Industry Co., which was going to build the smelter, plunged 9.2 percent in Shanghai trading Wednesday.

Earlier this month, about 1,000 people protested to block a trash incinerator in Songjiang, near Shanghai, with no decision yet announced there on whether it will proceed. In December, local officials announced that they would stop a coal-fired power plant in Haimen, near Hong Kong, after an estimated 30,000 people marched to block the construction.

In September, a solar-energy company in Jiaxing, near Shanghai, was closed after demonstrations there. And in August, local officials in Dalian, in northeastern China, said a petrochemical plant would be closed and relocated after at least 12,000 people joined protests.

Thanks to the Internet — China has more Internet users than any other country — the success of the Shifang protesters seems to have been a lesson that reached across the country. "Shifang" was the most searched term on Sina Weibo, a Twitter-like microblogging service, on Tuesday and again Wednesday morning, before abruptly disappearing entirely from the list of frequently searched terms — a possible sign of censorship.

Several postings enthusiastically praising the Shifang protests Tuesday evening had been deleted by Wednesday morning, another sign of censorship. But more postings had replaced them.

"The Shifang news I put on Weibo yesterday, I just found out, has all been deleted," said one posting.

But the Shifang protests still may prompt copycats.

"Paying close attention to Shifang, because maybe the next one will be me, us," another Weibo posting said.

More stringent environmental rules and public pressure could erode some of the competitive advantage of Chinese companies. Multinationals have already tended to build cleaner operations in China, partly for fear of offending Chinese ultranationalists if there is a pollution scare and partly from public pressure in their home markets.

When Honda built a new auto-assembly plant in Guangzhou several years ago, for example, the company included a wastewater-management system that goes beyond the cleanup standards at many U.S. auto-assembly plants. Honda executives reasoned at the time that China would someday toughen standards, and it would be much cheaper to build to strict standards from the start instead of retrofitting later.

But a wide range of multinationals depend on Chinese suppliers for a huge variety of materials, and the costs of these materials could rise if the suppliers have to improve environmental compliance.

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Castro visit: Cuban leader Raul Castro arrived in China Wednesday for talks with President Hu Jintao and other leaders, his first visit to his country's key trading partner since taking office as president. China helped prop up the Cuban economy after the withdrawal of Russian aid in the 1990s. Bilateral trade totaled $1.8 billion in 2010, state-run website Cubadebate said.

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Includes material from The Associated Press