By Enrique Garcia

GUATEMALA CITY (Reuters) -An anti-corruption presidential candidate in Guatemala, whose surprise showing in a first-round election on Sunday means he will contest a runoff vote in August, said on Tuesday he would pursue closer relations with China if he wins.

"We need to work on our trade relations and expand them in the case of China," said Bernardo Arevalo in an interview with the Con Criterio radio program.

Guatemala, Central America's most populous country, has for decades opted for ties with Taiwan instead of the Asian giant.

Arevalo's comments follow China's success in recent years peeling off one-time allies of Taipei.

Guatemala is one of only 12 countries, plus the Vatican, with official diplomatic ties with China-claimed Taiwan.

In March, Honduras' leftist President Xiomara Castro opened relations with China after cutting ties with Taiwan.

Arevalo, a 64-year-old center-left congressman and son of a former president, said he seeks "to maintain good political relations with the Republic of China and Taiwan within the framework of mutual respect."

The candidate, who finished second in the crowded field behind Sandra Torres, the wife of another former president, stressed the need for a foreign policy based on Guatemala's interests.

"Let's be the owners of our foreign policy," said Arevalo, adding that no one else should dictate the country's position.

Torres will face Arevalo in the August runoff. She has promised to maintain Guatemala's ties with Taiwan.

In a statement to Reuters, Taiwan's foreign ministry said it would "continue to explain" the results of cooperation between Taiwan and Guatemala to both presidential candidates.

Taiwan would "actively seek the support of the two candidates for the traditional friendship between Guatemala and Taiwan", the ministry added.

In April, Taiwanese President Tsai Ing-wen visited Guatemala a week after the rupture with Honduras. Guatemala's outgoing president, conservative Alejandro Giammattei, followed up with a visit to Taiwan later that month, promising to deepen ties.

The United States, Guatemala's top trading partner, has tried to stem Taiwan's diplomatic losses in the region.

A defection by Guatemala would leave tiny Belize as Taiwan's last Central American ally.

(Reporting by Enrique Garcia; Additional reporting by Ben Blanchard in Taipei; Writing by Brendan O'Boyle;Editing by Sandra Maler, Robert Birsel)