Methamphetamine is being doled out to North Korean construction workers in a bid to speed up progress on a skyscraper in the capital city of Pyongyang, according to reports.

Project managers are dispensing the stimulant known as crystal meth or "ice" to builders, as pressure to complete a 70-storey apartment block mounts, a North Korean source has alleged.

"Project managers are now openly providing drugs to construction workers so that they will work faster," the source told Radio Free Asia.

"Project managers at a building site in North Korea's capital Pyongyang are openly supplying their exhausted work force with powerful methamphetamines called 'ice'. [They] are undergoing terrible sufferings in their work."

Hundreds of thousands of construction workers are believed to be working on the skyscraper, which forms part of a 60-building development on Pyongyang's Ryomyung Street.

Rumours that these workers have been dispensed drugs were fuelled when graffiti was found on one of the building sites. It reportedly reads "Pyongyang speed is drug speed".

When inhaled, crystal meth increases alertness and lowers inhibitions, but can also induce confusion and aggression. The effects can last for up to 12 hours.

Long-term risks for users include an increased chance of heart attack, brain damage and psychoses.

North Korea announced it was ushering in a "great golden age of construction" as one of a series of patriotic slogans revealed at the start of 2015.

The country's long-anticipated Ryugyong Hotel, which was expected to open in 2013, is still not complete. Leader Kim Jong-un commissioned Hong Kong firm PLT Planning and Architecture to design a new airport for the capital the same year.