BAKU, Azerbaijan (AP) — Azerbaijan's emergency service says 19 tourists visiting one of UNESCO's newest World Heritage sites have been injured after strong winds knocked down a massive branch from a nearly 500-year-old Oriental Plane tree.

It says the accident took place Sunday at the Khan's Palace in the historic city of Sheki, located on the ancient Silk Road that passes through the Caucasus Mountains.

The agency says a branch measuring about 50 centimeters (nearly 20 inches) in diameter fell on a group of tourists, leaving at least four people in critical condition. Officials say the tourists included two Russians, five Syrians and 12 Azeri citizens.

Sheki's city center and the Khan's Palace were added to the World Heritage site list just a week ago.