Sky's special correspondent Alex Crawford takes one of the final trips into and out Severodonetsk, which some call "the next Mariupol". It appears that Russian troops are in control.

The time is running out for thousands of people trapped in Severodonetsk, and they are facing a very difficult task.

One of our last trips was made before heavy shelling forced the Ukrainian military to close the bridge that allowed us to enter the city.

As the two sides fight for control, the city has been under sustained and intense bombardment in the last few days. There has been no respite from the fighting day and night.

It seems that the Russian troops are invading our city. They are trying to take this city with all they have - shelling and pounding, missile strikes, and signs that they have ground troops on the city's perimeters, but also inching their way in.

Russian soldiers have fired on volunteers who were trying to provide water and food to those trapped by the fighting.

One of them was shot in the arm, but they fled to safety at nearby houses where they were delivering assistance. Those inside bolted from their doors and refused entry. Although it is not known why they did this, it is a sign of the fear, suspicion, and split loyalties that have become a major focus for the Russian military.

It could get worse

However, the Ukrainian troops are far outnumbered. In some parts of the Donbas, the president of Ukraine has warned that there could be seven to one.

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It seems like only a matter of time that this important city in the Donbas region of Luhansk will fall under Russian control. If it happens, Russia will likely use it to launch further moves into Donetsk and the Donbas, which are the two areas that make up the region.