The Trans-Caspian trade route, also known as the "Middle Corridor", allows goods to flow from China to Europe while bypassing Russia.

The work, expected to be finished this year, will "increase the load capacity of ships in the port of Aktau and transport along the Trans-Caspian transport route", a spokeswoman from Kazakhstan's transport ministry told AFP.

Russia's invasion of Ukraine and the imposition of massive Western sanctions have pushed Europe to look at alternative ways of securing imports from China and the rest of Asia.

The route crosses Central Asia, the Caspian Sea, the Caucasus and then Turkey.

The European Union announced earlier this year it would invest 10 billion euros ($11 billion) to develop the route through Central Asia.

Freight volumes are expected to triple by 2030 to 11 million tonnes if infrastructure can be improved, according to the World Bank.

But falling water levels in the Caspian Sea -- which needs to be traversed to get from Central Asia to the Caucasus -- jeopardise the route's viability.

Shallower waters make it trickier for larger vessels to ferry cargo.

"If we do not carry out dredging work by the end of the year and the sea level continues to fall, navigation will remain inefficient," an official at the Aktau port told Kazakh state media earlier this month.

Kazakh scientists reported in January an "acceleration" in declining water levels.

The Caspian Sea, larger than Germany, is surrounded by Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan.