Ukrainian servicemen and fleeing residents described ferocious fighting on Kyiv's northwestern edge Monday that could soon spread to the besieged capital.

"There is real street fighting now," a Ukrainian paratrooper lieutenant who agreed to be identified as Stas told AFP in the flashpoint town of Irpin.

Bursts of automatic gunfire and blasts of exploding shells rang out as he spoke on the 12th day of the Russian invasion.

"In some places, there is hand-to-hand combat," said Stas.

"There is a huge column -- 200 men, 50 light armored vehicles, several tanks," he said of the Russian threat. "We are trying to push them out, but I don't know if we'll be fully able to do it. The situation is very unstable."

- Special forces -

The industrial town of Irpin represents the outgunned Ukrainian forces' last point of resistance against the Russian assault on Kyiv.

The Russian offensive began with missile strikes and a paratrooper deployment in Kyiv's more distant suburb of Gostomel on February 24.

Ukrainian soldiers beat back the initial push and destroyed some of the first Russian armoured vehicles.

But the Russians sent in reinforcements from Belarus that reached the outer reaches of suburban Kyiv at the start of last week.

The offensive has been gaining momentum ever since.

Russian ground forces seized a series of settlements around Gostomel and used incessant shelling attacks to reach further south into Irpin's sister town of Buchau.

"On Friday morning, there was a Ukrainian flag over Bucha, and then the Russian teams started coming in," said local resident Vitaliy Shichko.

The 47-year-old had one bandage over two bullet wounds to his left wrist and another over purple bruises on the left side of his face.

"At first, they seemed to be sending in people they weren’t afraid of losing," Shichko said.

"But when I was hiding in the basement, the Russians who found us were serious, well-equipped, with torches and full communications –- basically, special forces."

- 'Hoping to be saved' -

Much of Bucha now stands in ruins.

The town is still being pummelled with mortar fire and dark smoke towers over its horizon.

But residents and Ukrainian soldiers told AFP that almost everyone who was strong enough to walk has now fled.

"The older people, those who cannot use their feet, they remain," resident Marina Manfyorova said while rushing toward evacuation buses waiting on the Kyiv side of a river splitting the capital from Irpin.

"They are still hoping to be saved."

The Russian push into Irpin began with bombing raids that sent the first big wave of residents fleeing on Saturday morning.

Russian tanks and armoured vehicles could be seen moving on Monday within two kilometres (just over a mile) of Kyiv's city limits.

Lieutenant Stas said the Russian had positioned four assault squadrons across the western half of Irpin.

"Now, our artillery is hitting them," he said.

- Snipers -

Several witnesses said the Russians had installed snipers into a block of highrises overlooking deserted streets and muddy fields used by residents to make their final dash into Kyiv.

"There is a sniper in that blue building," soldier Oleksiy Cherikalov said with a look over his right shoulder.

The 40-year-old was taking a day off duty to evacuate his own family from Irpin.

But even he seemed stunned by the scale of the seemingly random violence.

"That sniper has been shooting at us all day," he said.

Other witnesses and soldiers said the Russians had forced some people from their homes in order to establish new shooting positions.

AFP was unable to reach Russian soldiers who could comment because of the dangers of crossing the fast-moving frontline.

"The Russians are positioning themselves in residential buildings, apartments, shops," said soldier Konstantyn Lokhmitskiy.

"After that, they started shooting exclusively at civilians," the 38-year-old alleged.

"I also fought. This is my third war. But this never used to happen," Lokhmitsky said. "No one shot at civilians back then."