As Southeast Asia's leaders gathered this week for a summit, their currencies soared, some hitting nearly two-year highs.

The cause was not anything they said, but rather speculation that Beijing was poised to let the yuan rise.

It was a fitting reminder of the lengthening shadow that China casts over the region's economic affairs.

China's growth has helped lift its neighbors from the gloom of the global financial crisis, but fears remain that it is, if anything, too strong, a fierce and unbeatable competitor.

"What I've said all along is that one of the major drivers for the world's recent economic recovery, and in Asia in particular, has been the robustness of the Chinese economy," Korn Chatikavanij, Thailand's finance minister, said at the summit of the Association of Southeast Asian Nations (ASEAN) in Vietnam.

But on the touchy subject of how Beijing has held down the yuan to aid its exporters, Korn pulled no punches.

"There is no way that you can argue that it does not cause any imbalance," he said. "Clearly, you have got a situation whereby at least one major currency is being managed in such a way that it doesn't reflect its true value."

A China-ASEAN Free Trade Agreement came into effect in January, forming an economic bloc of 1.9 billion people.

While China's vast market is a big lure, some Southeast Asian businesses, particularly in Indonesia, worry about an influx of cheap goods. With Indonesian anger rising, China agreed this month to provide $1.8 billion in soft loans.

But the surprising truth about economic ties between China and Southeast Asia is that trade and investment flows are weak.

Goods sold to Chinese consumers account for less than 10 percent of total exports by each of the five largest ASEAN economies — Indonesia, Malaysia, the Philippines, Singapore and Thailand — according to estimates by UBS.

Moreover, Chinese investment in ASEAN countries was $8 billion as of late 2008, just 2.4 percent of the region's total stock of foreign direct investment.

"The direct impact is not that large. But that is not to say that China's leap onto the world stage and massive export performance has not had an impact. It has," Ed Teather, a UBS economist in Singapore, said.

"It is forcing ASEAN's economies to change," he said.

Before 2000, Southeast Asia had steadily increased its share of the global export market, but it has been flat since China joined the WTO in 2001. China's share of the global export market has, by contrast, jumped to 10 percent from 4 percent.

Southeast Asian nations have honed different strategies for living next to the Chinese manufacturing juggernaut.

Singapore has ramped up service industries. Overseas Philippine workers have made remittances a pillar of the economy. Indonesia's commodities sector has boomed on China's voracious appetite, while its factories have grown much more slowly.

The region may be in for more profound change if China is successful in its economic restructuring efforts, stimulating more domestic consumption while also increasing incomes.

For advanced economies, such as Singapore, Chinese consumption is already helping to power exports, ANZ economists Paul Gruenwald and Wei Liang Chang wrote in a report this week.

"We found evidence that the Chinese consumer is now playing a statistically significant role in intra-regional trade," they said. "The implication is that Asia has at least partially de-linked from the West."

For poorer countries in Southeast Asia, rising Chinese wages could give them new opportunities in low-end manufacturing.

"As China's labor gets a little bit more expensive over time, you will have a second wind for places like Vietnam and perhaps the Philippines," Teather said.

A stronger yuan will, over time, be part of the process of making Chinese goods more expensive. Southeast Asian governments, which stand to be big beneficiaries, have largely refrained from criticizing Beijing's currency policy.

Along with gaining some market share at China's expense, yuan appreciation would permit central banks in the region to let their currencies climb without fear of losing competitiveness.

The Malaysian ringgit, for example, considered a good proxy for the yuan, spiked on Thursday after a report that China was on the cusp of announcing a revaluation. The Indonesia rupiah and the Thai baht also rose sharply.

But Indonesia's deputy central bank governor, Hartadi Sarwono, said the yuan did not come up for discussion at the summit in Vietnam, because it was a global issue, being fought over by Washington and Beijing.

"It's China versus the rest of the others. It's not really ASEAN countries," he said.