A man is in hospital after what London police are calling an assault at an apartment building in the city's southwest end.

Police and EMS were called to apartment 608 at 297 Baseline Road West around 10:30 a.m. Monday for a male suffering from a head injury.

The male was transported to the London Health Sciences Centre where police say he underwent emergency surgery and remains in guarded condition.

Investigators say the man had been assaulted in an altercation with three other males.

One male is in custody and an investigation into the role of the other men continues.

Police say the incident is not believed to be a random attack.

Anyone with information is asked to contact police at 519-661-5670 or Crime Stoppers.