Updated 10.55am

Russia's ground forces invaded Ukraine from several directions on Thursday, encircling the country within hours of President Vladimir Putin announcing his decision to launch an assault.

The situation is volatile and fast moving, but this is what we know at 0900 GMT: 

Heavy Russian tanks and other equipment crossed the frontier in a string of northern regions as well as from the Kremlin-annexed peninsula of Crimea in the south.

They were also advancing into the Western-backed government's territory along the eastern front, where a separatist insurgency has claimed more than 14,000 lives since 2014.

Ukraine's confirmed military death toll reached five a few hours after Putin launched the invasion.

But there were reports of major clashes across large parts of the vast eastern European country and the death toll seemed likely to climb throughout the day.

Ukraine claimed to have killed around 50 "Russian occupiers" while taking back control of the eastern frontline town of Shchastya.

AFP could not be independently confirm the claim.

Although Ukraine has been riven by conflict in the east, which has forced some 1.5 million from their homes, it had reported no fatalities along its southern border with Crimea for some years.

But the border guard service reported some of the heaviest fighting near Crimea, where the servicemen died in Russian missile and helicopter attacks.

Russia has heavily fortified its positions on the peninsula, where it has had military bases since its takeover in 2014.

After holding a series of emergency calls with world leaders, including US President Joe Biden, Ukraine's leader Voldymyr Zelensky convened a meeting of the top military brass.

Zelensky "gave orders to inflict maximum losses against the aggressor," Commander-in-Chief of the Armed Forces of Ukraine, Major General Valeriy Zaluzhny, said.

Presidential adviser Mykhailo Podoliak said Ukraine's forces were "waging heavy combat" and repelling Russian advances in some parts.

Kyiv airport bombed

Ukrainian officials said Russia was primarily targeting military infrastructure and silos, hitting a string of air fields.

These included Boryspil airport in Kyiv, the armed forces said.

Ukraine closed its airspace to civilian traffic. Tracking websites showed no civilian airliners within the country's airspace on Thursday.

The invasion was also staged from several positions in Belarus, where Russian armed forces have been holding massive military drills this month involving an estimated 30,000 troops.

But Belarus strongman leader Alexander Lukashenko said his forces were "not taking part in this operation".

Ukraine also claimed it had downed six Russian planes, a helicopter, and destroyed four tanks.

Moscow did not confirm suffering any casualties or other military losses.

In Ukraine's east, where AFP reporters heard violent explosions in several towns along the front, Russian-backed forces took control of several villages that had been under the government's control.

But Ukraine's armed forces claimed it had won back some areas in a counteroffensive.

Putin this week authorised sending "peacekeepers" into the rebel provinces, after recognising their independence on Monday.