By Francesco Guarascio

HANOI, Feb 25 (Reuters) - Vietnam's goods exports to the United States accounted for 30% of its gross domestic product last year, the highest share among U.S. top trade partners, a Reuters review of public data shows, making the country highly vulnerable to reciprocal tariffs.

The Southeast Asian nation experienced a surge in foreign investment after the first Trump administration started a trade war with Beijing in 2018, as foreign multinationals moved factories from China to its southern neighbour to avoid U.S. tariffs.

It hosts major operations of South Korea's Samsung Electronics 005930.KS and Taiwan's contract manufacturer Foxconn 2317.TW. Apple AAPL.O, chipmaker Intel INTC.O and footwear and apparel giant Nike NKE.N are among U.S. corporations which bet on Vietnam as a production hub for goods often exported to the United States.

The massive inflow of manufacturing investment has turned the Communist-run nation into a major node in global supply chains and significantly boosted its economic ties with the United States. Vietnam now directs 29% of its exports to its former foe, according to Vietnamese customs data.

Last year, with goods exports worth $142.4 billion, Vietnam became the sixth largest exporter to the United States after Mexico, China, Canada, Germany and Japan, United Nations commodity trade statistics show.

Shipments to the U.S. last year represented about 30% of Vietnam's GDP of $468 billion, based on IMF's estimates, the largest share for all U.S. trading partners.

Only Mexico, which is facing explicit threats from Trump of 25% tariffs, has a comparable exposure. It ships more than three times more goods than Vietnam to the U.S., with the total value of its exports accounting for 27.6% of its larger GDP.

By comparison, China's exports to the U.S. are worth 2.5% of its GDP, and Japan's 3.7%.

Vietnam's vulnerability is compounded by large trade imbalances that could make it stand out as U.S. officials study global reciprocal tariffs, which U.S. President Donald Trump has mandated to prepare by April.

Vietnam's booming exports, combined with limited imports from the U.S., made it last year the U.S. partner with the fourth-largest trade surplus, lower only than China, the 27-country EU and Mexico, according to U.S. trade data.

The country also "satisfies (other) criteria for tariff applications set by the White House", said Sayaka Shiba, a senior analyst at research firm BMI, noting that compared to the U.S., it has higher tariff rates, levies VAT, has non-trade barriers and is on the U.S. watchlist for possible currency manipulation.

(Reporting by Francesco Guarascio; Editing by Lincoln Feast.)

((Francesco.Guarascio@thomsonreuters.com;))