Seoul, South Korea (CNN) -- Seven crew members from a South Korean cargo ship remained missing Tuesday after the boat sank Monday in the South China Sea, the South Korean Foreign Ministry said.
Fourteen people have been rescued, according to the ministry.
The ship was headed from Penang, Malaysia, to China and disappeared after sending out an emergency signal Monday afternoon. While six South Koreans and eight crew members from Myanmar were rescued by nearby vessels, seven seamen are still missing.
The Foreign Ministry said it is still hopeful, as one crew member was rescued at noon on Tuesday -- almost 20 hours after the ship requested assistance.
Hong Kong rescuers have deployed two helicopters and seven ships to help with the search and rescue operation, while two Chinese naval vessels were en route to the scene, according to the Foreign Ministry.
The 15,000-ton sunken vessel is the same ship that was hijacked by Somali pirates in 2008 when eight sailors were held captive for 37 days, according to South Korea's Yonhap news agency. The cause of the sinking so far is unknown.