At least 32 people have died of the disease so far this year, Health Minister Cesar Vasquez said on Monday.
There have been 31,300 cases recorded in the first eight weeks of the year.
"This is a grave problem," Vasquez said last week. "And it is getting out of hand."
Vasquez said Peru's typical response to the disease had been "overtaken" by factors such as climate. The El Nino weather pattern has caused warm temperatures and heavy rainfall.
"The weather has created a perfect breeding ground for mosquitoes to reproduce more quickly and become a more frequent vector of the disease," he added.
What does the declaration entail?
The health emergency was declared in 20 of Peru's 25 regions.
Most of the cases so far have been in the north of the country.
The move will enable the government to transfer funds more quickly to affected regions and more easily deploy doctors and nurses.
Dengue causes causes symptoms such as fever, nausea, vomiting, fatigue and body aches.
It is largely transmitted through bites from infected mosquitoes.
