(Reuters) - "China's gas pipeline will be burned," chanted a group of protesters in Myanmar this week on the route of a Chinese pipeline.

Hailed by China as a symbol of "mutually beneficial cooperation", the pipeline has become a target for public anger over perceptions Beijing is backing the junta that seized power in a Feb. 1 coup.

The rise in anti-China sentiment has raised questions in Myanmar business circles and in China, not only over the surge of Chinese investment in recent years but for billions of dollars earmarked for a strategic neighbour on Beijing's "Belt and Road" infrastructure plan.

"Chinese business, Out! Out!," the dozen or so protesters shouted in Mandalay city, a staging point on pipelines across Myanmar from the Indian Ocean to China. Social media carried many more threats.

The gas pipeline, which carries gas from Myanmar's offshore fields, opened in 2013, as Myanmar's military was starting democratic reforms. The $1.5 billion 770-km (480 mile) oil pipe alongside, bringing crude mainly from the Middle East, started in 2017 under the government of elected leader Aung San Suu Kyi, who is now detained and facing an array of charges.

A PetroChina official who declined to be identified said there had been no problems with the operation of the oil pipeline - the only source of crude for the state energy giant’s refinery in Kunming, Yunnan province.

Protests over the pipeline flared after a Myanmar government document leaked from a Feb. 24 meeting showed Chinese officials had asked Myanmar's junta to provide better security - and intelligence on ethnic minority armed groups on the pipeline route.

Reuters was unable to reach officials in Myanmar for comment on the document.

"Safeguarding the security of bilateral cooperation projects is the common responsibility of both China and Myanmar," China's foreign ministry said in response to questions on the document, reiterating its call for "all sides in Myanmar to exercise calm and restraint" and to resolve their differences.

"This would also benefit the secure operations of bilateral cooperation projects," it said.

China did not immediately respond to a question on anti-China sentiment.

HOSTILE OPINION

Billions of dollars had been earmarked for such projects, including an economic corridor ending at a $1.3 billion deepwater port, industrial zones, a new city next to the commercial hub of Yangon and a railway to the border.

"Hostile public opinion will inflict long-term threats and damage to China’s plan," said Yun Sun, director of the China Program at the Washington-based Stimson Center.

She pointed in particular to the damage done to Beijing's reputation over the Myitsone Dam project, which was shelved in 2011 amid a local outcry - prompting a concerted effort by China to cultivate the public as well as political leaders.

"Public opinion has been treated as a priority for China’s policy in Myanmar," she said.

Efforts in recent years included everything from donating school backpacks to sponsoring inspection trips to China for officials - though a 2018 survey in Myanmar still found an "explicit bias" against Chinese investments.

China had also tried to keep close to Suu Kyi, while maintaining ties to the army that overthrew her.

Balancing the relationship has become even more precarious.

While Western countries have condemned the coup, China has not even described it as one - in line with the generals' wishes. Its call for restraint from both sides draws scorn from opponents of the coup who point to the killing of more than 60 protesters. One policeman has died, the army says.

"China shame on you. Stop supporting the theft of a nation," read one protest placard outside the Chinese embassy before Myanmar security forces cordoned it off.

SUSPICIONS

No matter how outlandish, allegations of Chinese involvement have swirled on social media.

Some said they had seen soldiers with Chinese features or heard some speaking Mandarin. Suspicions were raised by an increase in night-time flights to China - flights the state airline said carried seafood for the Lunar New Year holiday.

Unsubstantiated claims surfaced that the planes were bringing in soldiers or technicians to install an internet firewall - an idea dismissed by the junta and described as "nonsense" by the Chinese ambassador.

Concerns that anti-Beijing sentiment could turn on Chinese businesses has prompted some to reconsider their positions - especially as anti-coup protests and strikes strangle the economy.

"They can only vent on the Chinese people on the ground," said one Chinese businessman who gave his name as Ran and is now seeking a way out - while saying he had not faced any personal attacks.

Myanmar also has a substantial minority with Chinese origins, whose older members remember anti-Chinese riots in 1967 in which an estimated 30 people were killed. Some younger members, however, have taken a conspicuous stand with the protesters.

"Our elders worry about the Sinophobic posts - things on Facebook like 'the Chinese will be the first people to be beaten' but it's only a small number of people making them," said Aung Aung, 23, a founder of the Young Burmese-Chinese Association.

"The people know where we stand. We want to get democracy back."

(Writing by Matthew Tostevin; Editing by Robert Birsel)