According to officials, steps were taken to keep swimmers safe by closing Nai Thon, Nai Yang and Layan beaches of Thailand's famous tourism destination Phi Phi lsland on Monday, Xinhua news agency said.
Other beach resorts have posted notices to warn about the dangers of Portuguese man o'war and box jellyfish and set up First Aid stations to deal with any emergency.
The Portuguese man o'war jellyfish resembles a blue or purple cap of the Portuguese naval soldiers. They are among the world's most venomous marine species whose stings are painful and even fatal in some cases.
However, so far no sting has been reported.
During the monsoon season, rain, wind and storms often bring jellyfish and other unexpected marine creatures closer to the shore.
Teams from a national park inspected the beaches where a swimming ban was imposed, along with other beaches in Phuket, covering a distance of six km. They reportedly collected a total of 145 live and dead Portuguese man o'wars.
Swimmers who are stung by such creatures are advised to pour salt water over the affected area, instead of scrubbing or applying suntan creams.
The Phi Phi island features beaches and clear water that have earned it a protected national park status for its natural beauty.
Tourism on the island exploded after movies were shot here. The island offers scuba diving, snorkeling, kayaking and other marine recreational activities.
