Police described it as a "random attack by opportunists".
But it has prompted the peak medical body in the city to call for swift justice for this "lovely family" of doctors.
Dr Rongap was attacked by a group of men with bush knives and shot at close range, said Lae Metropolitan commander Anthony Wagambie. He said one suspect, from East New Britain, had been arrested while a further five were still being hunted down by police.
Wagambie said the suspects were repeat offenders who had been terrorising motorists by carrying out random armed robberies.
Dr Rongap, who was a specialist surgeon at the Angau Memorial Hospital, is survived by his wife and two children, all of whom are also medical doctors.
Wagambie said the doctor was also attacked with a bush knife after taking the gunshot between 7.30pm and 8pm on Saturday at Centre Market after dropping off a friend.
PNG media outlets reported that the president of the Lae Branch National Doctors' Association, Dr Joseph Garap, had appealed to the law enforcers to use the full force of the law to bring to justice the suspects.
Dr Garap said the late Dr Rongap's son Dr Alponse Rongap Jr recently completed his Masters in Medicine and was now a specialist surgeon working at Angau Memorial Hospital.
"It is beyond belief that such a tragedy would befall this lovely family. Who in their right mind would have predicted such a tragic ending to his life?" he asked.
"It is in the strongest terms, we his colleges, both in Lae and throughout PNG, condemn this inhumane act of murder and call for an immediate search of this murderer," said Dr Garap.