Following reports of the jellyfish in the area, local authorities ordered increased monitoring and safety warnings for residents and tourists.
At the request of Quang Ninh's Department of Agriculture and Environment, scientists from the Haiphong branch of the Institute of Oceanography examined images and videos of the jellyfish and consulted Japanese experts.
They identified it as Chrysaora sp., a genus of stinging jellyfish in the family Pelagiidae.
The jellyfish typically has a bell about 15-20 cm in diameter, with long tentacles that can extend two to three times the bell's diameter. Its translucent or pale yellow bell often has dark brown, star-like markings.
Contact with the tentacles can cause sharp pain, burning or stinging sensations, while affected skin may become red and swollen or develop tentacle-shaped marks. More severe reactions can include blisters.
Chrysaora jellyfish have been recorded in coastal waters across Vietnam. They can occur in relatively high densities between June and August, particularly in waters with relatively high salinity and clarity.
During surveys off Tra Co in Quang Ninh in August 2019, scientists recorded two species of stinging jellyfish near the surface at densities of about 30-50 individuals per 1,000 cubic metres of seawater.
Scientists said understanding the jellyfish's biological characteristics, seasonal occurrence and ability to cause skin irritation could help authorities and the public respond to their presence, particularly at beaches and tourist areas.
Quang Ninh authorities have stepped up warnings to hotels, tour operators, guides and visitors around the Hon Gai beach and asked tourism businesses to take measures to protect swimmers.
Beach operators have been instructed to install fine-mesh nets around swimming areas, extending from the surface to near the seabed, to prevent jellyfish and drifting tentacles from entering.
Teams equipped with protective gear will also be deployed to regularly remove jellyfish from swimming areas.
People stung by jellyfish should receive prompt first aid, while those with severe symptoms should be referred for medical treatment.
Local authorities have also been asked to monitor coastal waters and report any unusual appearance or sharp increase in jellyfish numbers for further action.
