The apartment block in Kuala Lumpur, Malaysia, where a man allegedly set himself on fire to protest wife's lesbian affair.

A Malaysian man is fighting for his life in hospital after allegedly setting himself on fire after discovering his wife was having a lesbian affair.

The 50-year-old husband, known only as Lim, set fire to himself in their Kuala Lumpur apartment when he found that his wife had been conducting an affair with her boss for 18 years.

The couple's 18-year-old son was surfing the internet at home when he heard his mother scream.

"He rushed out of the room and saw his father on fire and tried to put out the flames using water from the bathroom," said Assistant Commissioner Amiruddin Jamaluddin. "Neighbours also helped him."

The victim was rushed to Ampang Hospital where he remains in critical condition. His wife was being treated for burns to her legs.

The son denied claims that his mother had tried to kill his father and suspected that he was trying to kill himself instead, police said.

Relatives have claimed that the man wanted to kill his wife and three children, aged between eight and 18, but could not bring himself to do so.

The Malaysian government has been internationally condemned for its anti-gay rhetoric and policies. Human Rights Watch has criticised Kuala Lumpur for demonising LGBT people.