President Xi has arrived in Russia’s capital for a trip expected to last four days.

While in Moscow, Xi will join the celebrations of Victory Day, a Russian holiday marking the end of World War II.

At the same time, Ukraine launched a wave of drone attacks aimed at disrupting events in Moscow.

Moscow’s Mayor, Sergei Sobyanin, said Russian air defense took down at least 19 Ukrainian drones overnight.

Due to the drone attacks, several Moscow airports had to shut down temporarily. Russia’s main airline, Aeroflot, changed its flight schedules to deal with the situation.

Ukraine likely launched the strikes to throw off Russia’s preparations for the big holiday event.

A plane carrying Serbia’s President had to be rerouted to Baku, Azerbaijan after being denied access to airspace by Latvia and Lithuania. He later landed in Moscow despite the delays.

Russia’s military claimed it shot down more than 500 drones in just 24 hours. Airport closures affected about 60,000 passengers.

This is Xi Jinping’s 11th trip to Russia as president—more than he has made to any other country.

Russia’s foreign ministry said this visit is a major moment in the relationship between the two nations. Xi is expected to sign several deals to make the China-Russia bond even stronger.