Rescued passengers of a capsized tourist boat rest at a port facility in Phuket, Thailand, July 5, 2018.( Photo: VCG)

Until 2:30 p.m. (0730 GMT) local time on Friday, the death toll  rose to 21 after two boats carrying Chinese tourists were overturned by rough seas in southern Thailand, Thailand authorities said on Friday. The rescue efforts to find the remaining missing passengers continued. 

Among 127 Chinese passengers, 21 were confirmed dead, 78 rescued and 33 were still missing, according to CCTV news.

The boats capsized on Thursday afternoon after encountering rough seas.

Early Friday, helicopters, police and fishing boats were deployed to assist the search for those missing.

"We will conduct air searches and send divers to check inside the sunken Phoenix boat," said Governor Norrapat Plodthong.

"Police investigators said most of the tourists were wearing life jackets," when the boat went down, he added.

"Eleven are injured, of these two are in serious condition," the governor also said.

The Thai maritime department said the injured were receiving treatment in hospital.

A Chinese consular official meanwhile arrived at the operations center in Phuket to monitor the rescue effort.

The Phoenix was among several boats that appeared to have ignored a severe weather warning in place since Wednesday to take tourists on day-trips to the islands that dot the seas off Phuket.

Besides the capsized vessels, an additional 10 pleasure boats were stranded at sea and being attended to by rescue vessels from the police and navy, according to Governor Norrapat.

Two passengers were still apparently unaccounted for from another stricken ship, he said.

The "Phoenix" was returning to Phuket from the popular snorkeling spot of Koh Racha at around 4:00 p.m. local time on Thursday when a storm hit, according to the captain, who identified himself as Somjing Boontham in a televised interview.

He said the boat was hit by a five-meter-high wave that flooded the boat, which started to slowly keel over, prompting him to warn passengers to put on life jackets and trigger inflatable life rafts.

Phuket is a magnet for overseas visitors including Western sun-seekers and huge numbers of Chinese tourists who make up the bulk of the 35 million people expected to visit the kingdom this year.