A school of 10 blacktip reef sharks was spotted hunting smaller fish in shallow waters near Koh Hong in Krabi's Thanbok Khoranee National Park on Sunday morning.
The sharks, each about one-metre long, were visible for over 30 minutes before they dived into deep water.
Jampen Phompakdee, head of the park's conservation unit, said it was rare for people to see sharks so near the beach.
They normally hunt in deep water at night around Koh Hong.
The park has prohibited fishing in the area of Koh Hong in order to help protect the marine life, and visitors and locals were told not to disturb or attack the harmless blacktip reef sharks.