Police are imploring drivers to slow down and drive safely after six people died on NSW roads over the weekend.

A three-year-old girl died after she was hit by a truck in South Grafton on Sunday morning, the latest victim in a horror 48 hours in which six were killed and many others were injured in separate crashes across NSW.

"We're imploring drivers today, as we do all the time, to watch your speed, think about what you're doing and be prepared each time you go for a drive," Traffic and Highway Patrol Assistant Commissioner Michael Corboy said on Sunday.

"The six people who are not with us have left families grieving in what ... we suspect would be avoidable accidents and these fatal crashes will continue to happen if people don't take the proper precautions."

Two young people, who were teen sweethearts, died on Saturday night after their car crashed into a power pole and exploded in flames in Matraville in Sydney's east, News Corp reported.

The car was believed to have been driven by a P-plate driver and police will nvestigate the possibility it was speeding before the crash around 10.30pm.

A 51-year-old man died at the scene of an accident on the Oxley Highway at Mt Seaview, 80km west of Port Macquarie, after a motorcycle crash around 2pm on Saturday.

Earlier, a 27-year-old woman was killed in a single-vehicle accident in Wee Waa, and near Bathurst a 50-year-old woman was killed and a 51-year-old man was seriously injured in a motorcycle crash.

Numerous others were taken to hospital after other crashes over the weekend.

The 31-year-old truck driver involved in the death of a three-year-old girl underwent mandatory testing, with police investigations ongoing.

Assistant Commissioner Corboy said police would investigate whether speed and alcohol were factors in the weekend's fatal crashes.

AAP