Police have shot and seriously injured a man who allegedly ran at them with a samurai sword in Brisbane's northwest.

Police say the man threatened officers who attended a Glenlyon Drive address in Ashgrove at around 8.30pm on Thursday, causing police to shoot at him.

The man, believed to be aged in his 40s, was taken to the Royal Brisbane Hospital in a serious condition.

The man was armed with a samurai sword and had threatened his partner with it before being shot, the ABC reported.

The Queensland Police Ethical Standards Command has commenced an investigation.