Police in Helsinki have issued a warning about water safety after a young man was taken to hospital to be treated for injuries sustained in a jet ski accident on Saturday.

"Jet skis are extremely powerful and can go really fast. Few people have the skills to handle them at high speeds, and the situations can be life-threatening," Sergeant Panu Kanniainen wrote in a press release.

Police said the jet ski involved in Saturday's incident was travelling at high speeds between Vasikkasaari and Koivusaari off the coast of the capital when it overturned, throwing the two passengers into the water.

There have been several similar near-misses in the waters around Helsinki in recent weeks, police said, adding that many people who rent jet skis do not understand that the crafts are "not toys" and can cause serious damage.

Finland's coast guard has previously noted that people on jet skis have been spotted following in the trail of ferries from Tallinn, saying such activity was "very dangerous".

Police are investigating Saturday's incident as a suspected case of endangering traffic safety.