The issue particularly affects younger demographics living in cities, newspaper Berlingske reports.
The trend has now persisted for a number of years, causing medical organisations to raise concern over the issue.
Medical journal Ugeskrift for Læger has described the situation as an “epidemic”, as has research institute SSI, which monitors the spread of infectious diseases.
Bjarne B. Christensen, general secretary with the Danish Family Planning Association (Sex og Samfund, DFPA), says that doctors' views on the issue should be taken seriously.
“It is very concerning that we again this year have seen an increase in chlamydia as well as gonorrhoea and syphilis,” Christensen told Ritzau.
An increase in cases of gonorrhoea in Denmark was first recorded in 2015 and continued in 2016, the year of the most recent available figures.
In 2016, 3,748 cases of gonorrhoea were recorded by doctors, of which 2,036 were men and 1,442 were women. That represented a 27 percent increase in one year.
Syphilis incidences have grown from just 22 in 1999 to around 700 per year.
SSI is currently working on a report into the number of cases of all three diseases in 2017, but can already see that numbers have not fallen compared to 2016, according to Berlingske's report.
Christensen called for new methods to be used to halt the trend.
“If we are to break this curve, we must work with young people to get the to use protection.
“The other thing we must do is to find the people who are infected. In addition to the 34,000 who have been confirmed to have chlamydia, an equally large group is thought to have it without knowing. So we have get better at making sure people are tested,” he said.
Both regional health authorities and educational institutions have a role to play in that effort, the DFPA general secretary added.
“The whole ongoing dialogue about safe sex is basically non-existent after school age, because youth education institutions don't have sex education.
“So the context in which young people can be reached out to is not good enough,” he said.