A new law has come into force in Norway making the purchase of sex illegal.
Norwegian citizens caught paying for prostitutes at home or abroad could face a hefty fine or a six-month prison sentence, authorities say.
The prison sentence could be extended to three years in cases of child prostitution.
The Norwegian authorities say they want to stamp out sex tourism and street prostitution by targeting clients rather than prostitutes.
"We think buying sex is unacceptable because it favours human trafficking and forced prostitution," deputy Justice Minister Astri Aas-Hansen was quoted as saying by the AFP news agency.
The tough new measures go further than similar ones introduced by other Nordic countries such as Sweden and Finland.
Norwegian police have been authorised to use wire-tapping devices to gather evidence.
There has already been a visible decrease in women working on the streets of central Oslo, local media report.
Prostitutes will be offered access to free education and health treatment for those with alcohol or drugs problems.
The government had already launched a publicity campaign before the law came into force.
Critics of the new regulations say prostitution will simply be driven underground and will be more difficult to control.