Formerly based in Kyiv, GSC Game World has managed to move some of its staff to new offices in Prague, but many remain in Ukraine.

In a new video diary the company has shown how its staff are living and working in especially tight quarters.

Some of them say they have been sleeping in corridors for months, while others say their office space is a square metre squeezed between bathtubs and washing machines.

All of them rest well away from windows which could shatter under Russian artillery strikes.

The S.T.A.L.K.E.R. video game series is a first-person shooter set in the Chernobyl Exclusion Zone, where paranormal events are taking place.

Key developments:
• A senior US defence official told Foreign Policy magazine that Russia's options are limited while Vladimir Putin refuses to formally declare war on Ukraine. The Russian president still describes the invasion as a "special military operation", meaning he cannot draw troops from the general population
• Farmers in Odesa have started their grain harvest, but Russia's invasion will mean a global wheat shortage for at least three seasons, Ukraine's agriculture minister said
• There are reports of overnight shelling in the Kharkiv region and the UK Ministry of Defence has said Russian forces appear to have made small gains there for the first time in many weeks

The game was inspired by the novel Roadside Picnic and the classic film Stalker by Andrei Tarkovsky - with its title a nod to the cinematic masterpiece and a backronym for "Scavengers, Trespassers, Adventurers, Loners, Killers, Explorers and Robbers".

The game development is ongoing but staff are attempting to manage their work alongside volunteering, military service, and Russian strikes on civilian properties and residences.

"We have air raid sirens around the clock," said Tara Kukurian, one of the game's community managers.

During the video diary the voice of Anton Kukhtytskyi, the game's lead concept artist, can be heard saying: "So, cat, the working day begins with a siren?".

"During the bombing, we run to the bomb shelter," says Andrei Maksiuta, the game's voice director, over smartphone footage of someone running down a flight of stairs.

Oleksandr Levchenko, one of the game's animators, is from Mariupol where a months-long siege on the Azovstal steelworks bought crucial time for Ukrainian forces elsewhere to organise and secure Western weapons.

He said: "Since the start of the war I've had no contact with my parents. It is an indescribable horrible feeling, not knowing whether your loved ones are alive."

Makysym Tkachenko recorded a video of himself squeezed between a bathtub and a washing machine: "This is my office space now."

Dariia Tsepkova, one of the game's narrative designers, said she has lived and worked in a corridor for three months with a one-eyed dog rescued from Hostomel.

"It's not easy to write violent quests when there's a war outside your window," she said.

Read more: Defying the Russian missile bombardment to care for 600 dogs and 100 cats in Hostomel

Dmytro Iassenev, the game's lead AI developer, is among the team members who have joined Ukraine's armed forces.

"I never imagined a war in Europe in the 21st century," he said.

Oleksii Ivanov, another of the game's community managers, said he was "defending my country from the Russian aggressors" in a video message recorded for the diary.

In another recording, Maksym Hnatkov, a narrative designer on the game, said he would return to working on it following a Ukrainian victory.

The conflict is now at a critical juncture that could determine the course of the rest of the war, US officials have said.

"I think that you're about to get to the point where one side or the other will be successful," a senior NATO official told CNN

"Either the Russians will reach Slovyansk and Kramatorsk or the Ukrainians will stop them here. And if the Ukrainians are able to hold the line here, in the face of this number of forces, that will matter."