The missing man and woman vanished as they and a friend paddled around Gai Island, a well-known rock formation shaped like a rooster near the resort town of Ao Nang.
The pair was in a double kayak while the friend was in a solo kayak.
''We went paddling and my friends went missing,'' the third tourist, a man, told Phuketwan in halting English last night. He raised the alarm as soon as possible with local authorities.
When he learned the pair were missing, the Director of the Chaofa Krabi Rescue Centre, Nitipat Mongkhonprasit mounted a search.
Eight members of the centre's staff with Marine Police and Tourist Police were looking for the couple in darkness early today.
''Conditions yesterday were not dangerous during daylight but the wind has sprung up since nightfall,'' Khun Nitipat said. The searchers in two dinghies were using spotlights to try to find the Chinese couple.
The three friends arrived in Krabi from Shenzhen on Sunday and were staying at a family bungalow resort in Ton-sai beach.
''We were planning on going snorkelling tomorrow,'' the friend told Phuketwan shortly before midnight. ''I tried to call my friends on their mobile telephone but there was no answer.''
The pair were wearing life vests, he said.
The safety and security of Chinese tourists has become of greater concern in and around Phuket and Krabi following a series of drownings on beaches and snorkelling trips.