Northern Territory Police are investigating two separate fatal crashes that occurred yesterday in the Top End.

A woman was declared deceased after the vehicle she was travelling in collided with a bull just after 8pm, approximately 30 kilometres east of Daly River.

The driver, who suffered non-life-threatening injuries and returned a negative breath test, and the female passenger were transported to the Daly River Clinic by family members.

Police from Daly River and Adelaide River attended the scene and established a crime scene. Detectives from the Major Crash Investigation Unit are investigating.

Earlier in the day, just after 1pm, police responded to a single-vehicle rollover on the Carpentaria Highway, approximately 30 kilometres from Borroloola.

A Toyota LandCruiser carrying five occupants is believed to have rolled, resulting in the death of a 55-year-old woman at the scene.

The remaining occupants suffered non-life-threatening injuries and were transported to Borroloola for initial treatment before being transported to Royal Darwin Hospital. 

A crime scene was held overnight, and motorists can expect traffic diversions to remain in place.

Major Crash Investigation Unit Detective Senior Sergeant Mick Schumacher urged motorists to take extra care on Territory roads, particularly over the long weekend, with increased traffic expected.

"This is not a good start to what should be a weekend spent enjoying time with family and friends.

"Two lives have been lost on Territory roads in separate incidents in a single day.

"Please take care on Territory roads."