The Ministry of Health is warning of a rise in syphilis cases in New Zealand, and is calling for people to practice safe sex.

There were 470 reported cases of the STI in 2017, more than double the 2015 figure.

Ministry of Health director of public health Dr Caroline McElnay said the Ministry is committed to reversing the upward trend.

"Transmission of these STIs can be reduced by using condoms every time with casual sexual partners; and regular partners," she said.

"If you have unprotected sex, or more than one sexual partner, the Ministry of Health encourages you to get tested even if you don't have any symptoms."

Nearly 70 percent of cases were reported in men who have sex with men, however there's been a steady increase in diagnosed heterosexual males and females in recent years.

Syphilis is a serious bacterial infection that can cause significant complications. It's usually sexually transmitted but can be transmitted from mother to baby during pregnancy or birth, resulting in serious complications and sometimes death.

It can be treated and cured with antibiotics, but if not treated over time it can affect the brain, spinal cord and other organs. If untreated, it also increases the risk of catching HIV.

If you think that you have syphilis or are at risk of syphilis, see your doctor or local sexual health clinic.

Newshub.