The city's Ocean Safety and Lifeguard Services says it posted Portuguese man-of-war warning signs along Ala Moana and Waikiki beaches Monday.
An Emergency Services Department spokeswoman says were a handful of stings, mostly in the Waikiki area.
Paramedics were called for a 56-year-old man and a 5-year-old boy for sting cases and both refused transport.
Lifeguards were treating the stings on the shoreline.
By 4 p.m., there were no more stings and the signs were removed.