A Donetsk resident has uploaded footage of a massive blast next to an apartment block in the heart of the city. The eastern Ukrainian city, which has been under rebel control since the start of the armed conflict, has been encircled by government forces.

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The video, shot from the window of an apartment block across a courtyard, captures a momentary fireball next to a multistory development housing thousands of people.

It is unclear from the footage whether the explosion is the result of an artillery shell explosion or a flash of gunfire.

City authorities say that two people have been injured, and several apartments, gas pipes and cars have been destroyed by the government barrage, saying that residents of almost all areas in the city are within earshot of artillery fire.

Authorities say that a nine-story residential block in the center city has been hit, though it is unclear if this refers to the incident witnessed in the video.

"There is constant thumping that hasn't stopped throughout the day," reports RT's Paula Slier from Donetsk.

"It is difficult to tell who is doing the firing. On the one hand you have the Ukrainian army vowing to take back the city, but these anti-government fighters are also very active and are saying that they won't let the city surrender."

The Ukrainian Army has said that it plans to recapture the militant stronghold by the end of the week.

Resdnts of #Lugansk & #Donetsk say Ukrainian army use tanks, heavy artillery in new tactic of storming city & leaving, storm&leave, &repeat. — PaulaSlier_RT (@PaulaSlier_RT) August 19, 2014

“The Ukrainian Army is continuing its operation to liberate Donetsk. Thirty fortified posts have been set up around the city to cut off the terrorists’ access," said a statement from Ukraine’s National Security Council in Kiev, referring to the rebel militias as “terrorists,” as the Kiev government has insisting on doing since it began its military operation in April.

Up to 70 percent of Donetsk 1 million residents are thought to have abandoned their houses, with the rest in long queues for basic supplies such as food, water and medicine as the encirclement has tightened, and the infrastructure damage has mounted.

"This is a humanitarian crisis unfolding," reports Slier.

The UN says that by "very conservative" estimates more than 2,000 people have died during the rebellion and the subsequent government offensive, which has isolated and pushed back the militants into their strongholds in the past several weeks.