A man has been charged with dangerous driving causing death, six months after a mother and her baby son were killed in a two-car crash.

Christchurch woman Mon Chhetri, 37, and her son Aaron, 8 months, were killed in the smash near Twizel in the South Island shortly before 7pm on April 19.

Five others were injured in the crash on Twizel-Omarama Rd, State Highway 8.

Police said a 44-year-old man had been charged over the crash. He is facing two charges of dangerous driving causing death and four of dangerous driving causing injury.

Mon Chhetri and Tula Ram Chhetri with two of their daughters. Photo / Supplied
Mon Chhetri and Tula Ram Chhetri with two of their daughters. Photo / Supplied

He will appear in Oamaru District Court on November 23.

Police at the time said the driver of the car Chhetri and her son were travelling in had slowed as it approached an intersection with SH8. The vehicle then pulled out on the highway into the path of an oncoming vehicle travelling south towards Omarama.

Chhetri and her son died at the scene, and the driver and a 10-year-old girl were airlifted to hospital. Three passengers in the other vehicle were also taken to hospital.

Chhetri and her family were originally from Bhutan, and had come to New Zealand as refugees.

The crash happened after the oldest daughter, Srijhana, 18, had been dropped off in Dunedin for university.

Husband and father Tula Ram Chhetri, 44 was driving the car when the crash happened.

Friend and chairman of the Christchurch Bhutanese society, Akash Drukpa, said Mr Chhetri was a very careful driver.

"It's like a non-smoker getting lung cancer."

He described Mon Chhetri as a "lively lady" with a big heart.