Zelenskiy acted on Wednesday as emergency crews proceeded with round-the-clock efforts to restore power and heating supplies thrown into disarray, particularly in Kyiv, by a Russian attack last week.
Repairs to thousands of apartment blocks have been compounded by frigid weather, with night-time temperatures dipping close to -20C.
"The consequences of Russian strikes and deteriorating weather conditions are severe," Zelenskiy wrote on X.
"Overall, a state of emergency will be declared for Ukraine's energy sector ... Many issues require urgent resolution."
Speaking later in his nightly video address, Zelenskiy said not enough had been done to deal with the aftermath of the attacks and the state of emergency would allow authorities "more options and flexibility."
He called for the establishment of more centres where residents can stay warm and charge electronic devices, and said nightly curfews could be lifted in areas where the security situation permitted it.
The president said Kyiv had done considerably less than other major centres, notably Ukraine's second-largest city, Kharkiv, to prepare for the hardships inflicted by the attacks.
"Even in recent days, I do not see sufficient intensity," he said.
"This must be urgently corrected. Decisions must be made."
Kyiv Mayor Vitali Klitschko, who has previously been at odds with Zelenskiy over the defence of the capital, wrote on Telegram that city officials had to "work efficiently, making decisions and finding ways to implement them. Otherwise, the work will be done by those who are capable."
In his remarks, Zelenskiy said a permanent coordination headquarters would be set up in Kyiv, with Denys Shmyhal, the newly appointed first deputy prime minister and energy minister, overseeing the work.
He said work was under way "to significantly increase the volume of electricity imports into Ukraine."
He also urged the military to hold their positions along the 1200-km front line and diplomats to keep pursuing efforts on documents needed to secure peace.
"From our side, maximum productivity is required," he said.
"We expect the same level of energetic work from the American side. I personally very much expect this."
