Explosions and gunfire have been heard in a northern district of Kyiv, as invading Russian forces closed in, AFP reports from the ground.

Pedestrians ran for safety and small arms fire and explosions were heard in the Obolonsky area. The larger blasts could be heard as far away as the city centre.

Russian forces first arrived on the outskirts of Kyiv on Thursday when helicopter-borne troops assaulted an airfield just outside the city, close to Obolonsky, AFP reports.

As they arrived in Obolonsky, within the city, the Ministry of Defense's Facebook page urged civilians to resist:

We urge citizens to inform us of troop movements, to make Molotov cocktails, and neutralize the enemy.

Russia pressed its invasion of Ukraine to the outskirts of the capital Friday after unleashing airstrikes on cities and military bases and sending in troops and tanks from three sides in an attack that could rewrite the global post-Cold War security order.

Explosions sounded before dawn in Kyiv and gunfire was reported in the city center as Western leaders scheduled an emergency meeting and Ukraine's president pleaded for international help to fend off an attack that could topple his democratically elected government, cause massive casualties and ripple out damage to the globaleconomy.

Among the signs that the Ukrainian capital was increasingly threatened, the military said Friday that a group of Russian spies and saboteurs was seen in a district of Kyiv about 5 kilometers (3 miles) north of the city center. Police told people not to exit a subway station in the city center because there was gunfire in the area.

U.S. Secretary of State Antony Blinken said Kyiv “could well be under siege” in what U.S. officials believe is a brazen attempt by Russian President Vladimir Putin to install his own regime.