TAIPEI -- A decline in Chinese mainland tourists to Taiwan could trim the island's GDP growth, Taiwan's statistics agency has said.

If the number of mainland tourists to Taiwan declines 10 percent this year, the island's service revenue would shrink by 17.8 billion new Taiwan dollars ($560 million), according to the Directorate-General of Budget, Accounting and Statistics (DGBAS).

This represents a 0.1 percentage point fall in the islands annual economic output.

The estimate is based on figures showing that each mainland tourist spent $228 per day and stayed seven days in Taiwan on average in 2015.

Last year, some 3.44 million mainland visitors traveled to the island as tourists, representing about 80 percent of all visits from the mainland. Other visitors traveled for reasons including study and business.

The DGBAS called for paying close attention to the decline amid a lackluster growth outlook for the island.

The number of mainland tourists has plummeted since Taiwan's leader Tsai Ing-wen took office in May. DGBAS data showed that the monthly decline had widened from 10 percent in May to 36 percent in August.

A DGBAS official said indirect economic losses brought about by the decline was still being calculated.

The island's GDP increased by 0.23 percent on a quarter-on-quarter seasonally-adjusted basis in Q2, according to official data. On a year-on-year basis, GDP grew by 0.7 percent over the same the period.