Samsung Electronics Co. sought to reassure consumers in China that its phones are safe in the country, as surveys suggested that confidence was taking a hit in a critical market for the smartphone giant.

Chinese consumers have been critical of China’s exclusion from Samsung’s global recall of 2.5 million Galaxy Note 7 smartphones, which the company launched on Sept. 2 after it received reports of fires caused by defective batteries. Samsung has said the faulty batch didn’t reach China, but reports of phone explosions in China...