German President Frank-Walter Steinmeier was forced to take cover in an air raid shelter Tuesday during his first visit to Ukraine since Russia's invasion.

The trip came six months after the president, then under heavy criticism for his years-long detente policy with Moscow, was snubbed by Kyiv.

After arriving in the capital, he headed to the northern town of Koriukivka -- but was forced to take cover when sirens went off.

"We spent the first hour and a half in an air raid shelter," he said.

"That really impressed upon us the conditions in which people here are living."

Koriukivka was occupied by Russian forces at the start of the war. Russian troops have since pulled back but the town is facing a bleak winter due to damaged infrastructure and difficulties with essential supplies.

Steinmeier hailed the courage of the town's residents, who he said had "confronted tanks with their bare hands, and actually brought them to a halt".

The power supply has been partially restored, he said, and a local heating plant will be converted so it can operate with wood harvested locally.

On his arrival earlier in Kyiv, Steinmeier had pledged that Germany will "further support Ukraine: militarily, politically, financially".

He is scheduled to meet with President Volodymyr Zelensky Tuesday evening, before returning to Germany on Wednesday.

His trip was originally planned for last week but was cancelled at the last minute due to security reasons, sparking jibes as officials from other countries made the journey.

In the months after Russia invaded Ukraine, Steinmeier, a former foreign minister, was heavily criticised over his years-long rapprochement towards Moscow, which he has since admitted was a mistake.

His offer to visit Kyiv in April was snubbed, sparking tension between the two countries.

Steinmeier, a Social Democrat serving his second stint as German president, was a foreign minister in two of former chancellor Angela Merkel's governments.

He has been a leading advocate of the "Wandel durch Handel" (Change through Trade) concept, which argues that fostering close commercial ties can help spur democratic reforms.

Steinmeier also championed the controversial Nord Stream 2 gas pipeline between Russia and Germany, which has now been halted over Moscow's aggression in Ukraine.

But he has since admitted that his detente approach towards President Vladimir Putin had been misguided, and that there could be "no return to normal with Putin's Russia".

Zelensky meanwhile asked the international community to cover an expected budget deficit of $38 billion next year for his war-torn country, in an address via video-link to a reconstruction conference in Berlin.