A Christchurch man has been rescued by his neighbour just moments before his house burst into flames.

The fire happened on Barbadoes Street near the central city about 6.20pm on Wednesday night.

Lucas Lormans said he noticed smoke billowing from his neighbour's house and ran next door to find his neighbour sitting on a couch in his smoke-filled lounge.

He began yelling the man's name but he didn't respond.

A passer-by heard the commotion and ran into the house to help lift the man, who was described as being limp and unresponsive, to safety.

"It all happened so quick," Mr Lormans told Fairfax.

"It would've only been about another 30 seconds before he was in flames himself."

Shortly after the fire "exploded", bursting the windows.

The man was taken to Christchurch Hospital and is in a serious condition after suffering burns and smoke inhalation.

Christchurch senior station officer Nigel Brook praised Mr Lormans, saying he did a great job.