Russian forces fired missiles at several cities in Ukraine and landed troops on its coast on Thursday, officials and media said, after President Vladimir Putin authorised what he called a special military operation in the east.

According to early reports, Russia's ground forces on Thursday crossed into Ukraine from several directions, Ukraine's border guard service said, ndtv.com. reported quoting AFP.

Russian tanks and other heavy equipment crossed the frontier in several northern regions, as well as from the Kremlin-annexed peninsula of Crimea in the south.

Russian military said it had knocked out Ukraine's air defence assets and airbases, reports AP. PTI

More than 40 Ukrainian soldiers and around 10 civilians died in the first hours of Russia's invasion of Ukraine, an aide to President Volodymyr Zelensky told reporters on Thursday.

"I know that more than 40 have been killed and several dozen wounded. I am aware of nearly 10 civilian losses," presidential administration aide Oleksiy Arestovych told reporters.

Shortly after Putin spoke in a televised address on Russian state TV, explosions could be heard in the pre-dawn quiet of the Ukrainian capital of Kyiv.

Gunfire rattled near the capital's main airport, the Interfax news agency said, and sirens were heard over the city. Residents of Kyiv were lining up in front of bank TMs to pick up cash. The main thoroughfare was choc-a-block with outbound traffic as residents chose to move away from the city, a Reuters video showed.

"Putin has just launched a full-scale invasion of Ukraine. Peaceful Ukrainian cities are under strikes," Ukrainian Foreign Minister Dmytro Kuleba said on Twitter. "This is a war of aggression. Ukraine will defend itself and will win. The world can and must stop Putin. The time to act is now."

U.S. President Joe Biden, reacting to an invasion the United States had been predicting for weeks, said his prayers were with the people of Ukraine "as they suffer an unprovoked and unjustified attack", while promising tough sanctions in response.

"I will be meeting with the leaders of the G7, and the United States and our allies and partners will be imposing severe sanctions on Russia," Biden said in a statement.

At the United Nations, India called for an immediate de-escalation of tensions between Russia and Ukraine and cautioned that the situation was in danger of spiralling into a major crisis.

Equity benchmark Sensex crashed over 2,700 points on Thursday following a severe sell-off in global markets after Russia launched the military offensive. The 30-share BSE gauge plunged about 2,850 points during the session before closing at 54,529.91, registering a massive fall of 2,702.15 points or 4.72 per cent.

Initial estimates claimed that investors’ wealth tumbled by more than Rs 8 lakh crore in less than an hour of trade on Thursday. Amid investors getting spooked by the escalating tensions between Ukraine and Russia, the market capitalisation of BSE-listed companies crashed to Rs 2,47,46,960.48 crore at around 10.15 am.

At the close of trade on Wednesday, the market capitalisation, an indicator of the notional wealth of investors, was at Rs 2,55,68,668.33 crore. This reflected a wealth erosion of more than Rs 8.2 lakh crore.

End Nato expansion: Russia

Russia has demanded an end to NATO's eastward expansion and Putin repeated his position that Ukrainian membership of the U.S.-led Atlantic military alliance was unacceptable.

He said he had authorised military action after Russia had been left with no choice but to defend itself against what he said were threats emanating from modern Ukraine, a democratic state of 44 million people.

"Russia cannot feel safe, develop, and exist with a constant threat emanating from the territory of modern Ukraine," Putin said. "All responsibility for bloodshed will be on the conscience of the ruling regime in Ukraine."

No occupation: Putin

The full scope of the Russian military operation was not immediately clear but Putin said: "Our plans do not include the occupation of Ukrainian territories. We are not going to impose anything by force."

Speaking as the U.N. Security Council held an emergency meeting in New York, Putin said he had ordered Russian forces to protect the people and appealed to the Ukrainian military to lay down their arms.

Ukrainian President Volodymyr Zelenskiy said Russia had carried out missile strikes on Ukrainian infrastructure and border guards, and that explosions had been heard in many cities. An official also reported non-stop cyber attacks.

Ukranian air bases destroyed

Zelenskiy said that martial law had been declared and that he had spoken by telephone to Biden. Reservists were called up on Wednesday.

Three hours after Putin gave his order, Russia's defence ministry said it had taken out military infrastructure at Ukrainian air bases and degraded its air defences, Russian media reported.

Earlier, Ukrainian media reported that military command centres in Kyiv and the city of Kharkiv in the northeast had been struck by missiles while Russian troops had landed in the southern port cities of Odessa and Mariupol.

A Reuters witness later heard three loud blasts in Mariupol.

Russian-backed separatists said they had launched an offensive on the Ukrainian-controlled town of Shchastia in the east, Russia's Interfax news agency said, and explosions also rocked the breakaway eastern Ukrainian city of Donetsk.

Hours earlier, the separatists issued a plea to Moscow for help to stop alleged Ukrainian aggression - claims the United States dismissed as Russian propaganda.

Global stocks and U.S. bond yields dived, while the dollar and gold rocketed higher after Putin's address. Brent oil surged past $100/barrel for the first time since 2014.

'Decisive way'

Biden, who has ruled out putting U.S. troops on the ground in Ukraine, said Putin had chosen a premeditated war that would bring a catastrophic loss of life and human suffering.

"Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way," he said.

NATO Secretary-General Jens Stoltenberg condemned Russia's "reckless and unprovoked attack" and said NATO allies would meet to tackle the consequences.

‘In the name of humanity…’

U.N. Secretary-General Antonio Guterres, speaking after the Security Council meeting, made a last-minute plea to Putin to stop the war "in the name of humanity'.

High risk to safety, while Europe's aviation regulator warned against the hazards to flying in bordering areas of Russia and Belarus.

Russia suspended domestic flights at airports near its border with Ukraine until March 2, its aviation agency said.

Intense shelling since Monday

Shelling had intensified since Monday when Putin recognised two separatist regions as independent and ordered the deployment of what he called peacekeepers, a move the West called the start of an invasion.

In response to Putin's Monday announcement, Western countries and Japan imposed sanctions on Russian banks and individuals but held off their toughest measures until an invasion began.

The United States stepped up the pressure on Wednesday by imposing penalties on the Russian firm building the Nord Stream 2 gas pipeline and its corporate officers.

Germany on Tuesday froze approvals for the pipeline, which has been built but was not in operation, amid concern it could allow Moscow to weaponise energy supplies to Europe.

With reports from Reuters, PTI, New York Times News Service