Millions of people were left for hours without electricity on Tuesday when a huge power blackout hit cities in three Central Asian countries.

Areas of Kyrgyzstan, Uzbekistan and Kazakhstan were affected when a shared power line was disconnected.  It caused traffic jams, airport delays and other public transport disruptions across the nations.

The capitals of Kyrgyzstan and Uzbekistan as well as Kazakhstan's economic hub Almaty had suffered power cuts at around lunchtime local time, with media and officials reporting that the blackouts had extended far into the provinces of the three countries, Russian news agency RIA Novosti reported.

Reuters says many residents across the region lost access to tap water, heating, petrol pumps and the Internet.

The blackout happened in the late morning, with power restored in most areas by early evening.

The BBC says the outage has once again raised concerns about how vulnerable the 1970s-built power line is.

Kazakhstan has reportedly experienced power shortages before, following a boom in crypto-currency mining - the process by which transactions are verified and new "coins" made.  Miners moved to Kazakhstan after crypto-currency mining was made illegal in China late last year.

It is now home to one of the largest bitcoin mining farms in the world, where thousands of computers work to verify and check transactions, which puts pressure on the country's power grids.

Hydro-electric power is also used across the region, however it has been burdened by drought. 

The grids of the three post-Soviet republics are interconnected and via Kazakhstan are linked to the Russian power grid, which they can use to cover unexpected shortages.

But Kazakhstan's North-South power line, which links densely populated southern Kazakhstan and its two neighbors to major power stations in northern Kazakhstan and the Russian network, was disconnected on Tuesday morning due to "emergency imbalances" in the Central Asian part of the grid, Kazakhstan's national electricity provider KEGOS said.