Chinese officials say a remarkable improvement in Beijing's air quality is due to good policy.

The Chinese capital has become infamous for its heavy smog, which is thought to lead to widespread illness and discomfort.

But residents have been enjoying blue skies this year.

In recent months, air pollution has dropped significantly, and jokes about Beijing's pollution have given way to surprised expressions about the lovely weather.

"Since March it's been great. Every day I run home from work and it's not like it was last year," one Beijing resident told the ABC.

"At the moment the air is very good — it's actually getting quite hot," said another.

Levels of harmful PM2.5 particulates have dropped by a fifth, and the number of "heavily polluted" days has halved over the last five months.

Beijing moving away from coal to cleaner energy sources

Fang Li, the deputy director of Beijing's environmental protection bureau, said much had been done to address the problem over the last year.

"Over the past 12 months our efforts to clean up have actually been greater than at any time before," he told journalists at Beijing's air quality measuring centre.

"You've felt the standard of air improving."

The air quality in the city has improved dramatically since February 2014, when this photo was taken. ( ABC News: Stephen McDonell )

Mr Li said 476,000 older cars were denied registration last year, with hundreds of thousands more to come off the road.

Petrol quality has also been improved, he said, and larger polluting factories have been moved further away from Beijing — potentially to become somebody else's problem.

Recent weather has also seen wind hitting the inland metropolis, blowing away some of the harmful airborne particulates.

Zhang Wangcai, the deputy director of Beijing's department of energy, said Beijing is moving away from coal for electricity generation.

Two coal-fired power plants have been closed recently, and a new gas-powered plant has opened up.

Mr Wangcai said no more coal-fired electricity will be produced in Beijing by the end of 2016.

"If we're talking about Beijing, by next year all our local power plants will be using clean energy," he said.