China has agreed to pay for a new national stadium and library in El Salvador as part of an infrastructure package promised to the country after it switched allegiance from Taiwan to Beijing.

President Xi Jinping met with Salvadoran President Nayib Bukele on Tuesday during the Central American leader's first visit to Beijing since being sworn into office this summer.

"President Xi Jinping has just granted El Salvador gigantic, non-refundable cooperation, completely managed by our government," Bukele tweeted late Tuesday announcing the projects, including a large capacity "modern" stadium.

The two countries issued a joint statement saying Beijing would also pay for the construction of two water supply projects, as well as the "reconstruction and expansion" of the "Surf City" tourism area and La Libertad pier along El Salvador's coastline.

Officials also signed agreements on economic cooperation and a plan to facilitate Chinese tourism to El Salvador.

China has ramped up investment and infrastructure spending abroad in recent years, raising fears that countries benefiting from Beijing-backed loans are at risk of falling into its debt.

But Bukele said in another series of tweets on Wednesday that "some opponents" had tried to attack the deals signed with China, "alleging that it is a 'debt trap.'"

"What part of 'non-refundable' did they not understand? It's not a loan, but a donation," he said.

El Salvador recognised Beijing in August 2018, becoming the third country to abandon Taiwan that year, following the Dominican Republic and Burkina Faso.

In September this year the tiny island nation of Kiribati switched its recognition to Beijing just four days after the Solomon Islands made the same move, leaving Taiwan with only 15 countries in its diplomatic circle.

China and Taiwan have been governed separately since the end of a civil war on the mainland in 1949, but Beijing sees the self-ruled democratic island as part of its territory to be brought back into the fold.

Taiwan and China have been engaged for years in a diplomatic tug-of-war in developing countries, with economic support and other aid often used as bargaining chips for diplomatic recognition. While Washington also recognises Beijing, the US government said last year it was "deeply disappointed" at the break of ties between El Salvador and Taipei.