At 22:49, a fourth alert stated there was a "Street fighting threat. Street fighting is taking place in Kyiv. Don't go outside."

At 23:53 a series of all clear messages were then delivered to users' phones, which were connected to each of the previous Kyivalerts, individually declaring each threat clear.

In a separate post on Telegram, the Ukrainian Central Intelligence Agency said that due to the Air Alert application, the Radiation Hazard signal was played on loudspeaker devices in the Lviv region, and added there was no threat of radiation hazard.

If the alert app is not working, Ukraine's Centre for Countering Disinformation advises the public to turn on notifications on their smartphones, pay attention to sirens, and to only read official sources

Several leaders of other regions also posted on Telegram that the app had apparently been hacked and there was no local threat.

"Everything is calm in the region for now," said Svitlana Onyshchuk, the governor of the Ivano-Frankivsk Oblast. The app had reported a red-level air raid alert for the oblast in Ukraine's east, between 22:50 and 23:57.

The Vinnytsia regional head, Natalya Zabolotna, said there had been a cyber-attack on the Air Alert app and posted a warning on Telegram not to click on the link in the message, which could be a phishing attempt.

The Air Alert app is supported by the Ministry of Digital Transformation of Ukraine, and informs users instantly about the beginning and end of defence alerts. The ministry had earlier said the app was temporarily disabled for maintenance after it had "apparently been compromised". It urged residents to turn on their smartphones' emergency notifications so they could receive state-issued distress signals.

A few hours after the false alerts in Ukraine, Russia's ministry of emergency situations said its app had been subjected to "a massive cyberattack" which sent "fake information to the public".

No further details were given by the ministry or state media.

Ukrainian news outlet, UNN, reported the hack sent fake alerts of a nuclear threat inside Russia.

Atesh, a partisan Ukrainian group operating inside Russian held territory, said on its Telegram page that the app had been hacked, accompanied with laughing emojis.

A screenshot of a purported emergency alert published by Atesh, which has not been verified by the BBC, told users to "urgently" stock up on provisions for three weeks and take cover in basements. It also used obscene language. Atesh has been contacted for comment.

Thealerts occurred just minutes before the end of a localised ceasefire in Ukraine's front-line Kherson region, which was implemented last Tuesday and officially ended at 23:00 Sunday.

Fighting had continued elsewhere while the Kherson ceasefire was in place, to allow civilians to evacuate the Russian-occupied city of Oleshky.

Russia launched a full-scale invasion of Ukraine in February 2022.