People from parts of the region "don’t have that many places they can go that are visa-free and so China has now become one of the major places that they really travel to," Ethan Lin, Klook’s chief executive was quoted as saying by Bloomberg.
China has in recent months eased visa rules for nationals of Southeast Asian countries.
In March Thailand and China permanently waived visas for each other's citizens.
Since February China and Singapore have been offering a mutual 30-day visa-free stay.
China recently agreed to double visa exemptions for Malaysian tourists to 30 days. It started allowing Malaysian tourists visa-free stays for 15 days in December last year.
China is also a major source of tourists for Southeast Asian countries.
Thailand received the highest number of Chinese tourists in Southeast Asia at 1.75 million during the first quarter, followed by Vietnam and Singapore.