"In the last 28 days 401 people have died of malaria which has become endemic in the state," Halliru Idris, director of public health in the state's health ministry, told IRIN.
The death toll could be much higher because this figure does not reflect those who died at home, he said.
WHO has recorded up to 50,311 malaria cases in Katsina state since September 19, which Idris attributes to the unusually heavy rainfall recorded this rainy season.
"We have recorded high rainfall this year, which means more and more mosquitoes breed [in the standing water that results]," Idris said.
Malaria is an infectious disease transmitted by mosquitoes; symptoms include sharp fluctuations in body temperature, weakness, body aches, nausea and vomiting. It can be fatal if not treated on time.
According to the 2008 World Health Organization's annual malaria report, the disease struck between 35 million and 80 million Nigerians in 2006. One million people died from malaria in 2006, most of them children under five.
Rubbish piles, open sewers and ponds which provide good breeding ground for mosquitoes are common sights in most Nigerian cities.
In Jigawa state, also in the north, over 100 people have been hospitalised with malaria in Maigatari district in the last week, according to Tafida Abubakar, the state's health commissioner, who also linked the high rate to heavy rainfall.
Katsina public health director Idris said the government has deployed health workers to the five most-affected districts - Daura, Funtua, Ingawa, Kurfi and Bindawa - to fumigate mosquito-breeding areas as well as to treat mosquito nets to prevent further transmission.