An Armed Offenders Squad officer has described a hail of bullets as he attempted to rescue an officer shot in the head during a siege near Kawerau.

28-year-old Rhys Warren is on trial at the High Court in Hamilton charged with two counts of attempted murder, three charges of firing at police officers and wounding with intent to cause grievous bodily harm.

Constable Martyn Roe has taken the stand and described the events as he and five other officers entered the house to attempt to arrest Warren.

Constable Roe has described hearing a "very loud bang" before seeing Constable Regan Mauheni fall back with blood all over his face.

At that point he described the arrest mission as becoming a rescue mission, as he told his fellow officers to lay down cover fire through the wall as he dragged the 115kg Constable Mauheni to safety.

Warren will now cross examine Constable Roe.