A woman fell a height of one storey when she tried to flee a Qawra residence during a fierce argument involving two men early on Tuesday.
The police said the incident happened at 6.30am in Andrew Cuningham Street.
The argument involved a 38-year-old man from Serbia, a 31-year-old Maltese and the woman, a Briton also aged 31.
The Maltese man suffered some slight knife injuries as he ran out of the residence. The woman also tried to run away, through the balcony, injuring herself in the subsequent fall.
Both the Maltese man and the British woman were hospitalised, with the latter found to have suffered serious injuries.
The Serbian man was arrested in the apartment and is being questioned for allegedly threatening the other two with a knife, the police said.