How many Vietnamese fled from Vietnam during the war?

Last days of the Vietnam Conflict and American Disengagement: "In the early hours of April 30, the last US Marines left the embassy as hectic Vietnamese breached the embassy perimeter and raided the place. PAVN T-54 tanks moved into Saigon. The South Vietnamese resistance was light. Tank skirmishes began as ARVN M-41 tanks attacked the heavily armored Soviet T-34 tanks. PAVN troops soon dashed to capture the US embassy, the government army garrison, the police headquarters, radio station, presidential palace, and other vital targets. The PAVN encountered greater-than expected resistance as small pockets of ARVN resistance continued. By now, the helicopter evacuations that had saved 7,000 American and Vietnamese had ended. The presidential palace was captured and the Vietcong flag waved victoriously over it. President Duong Van Minh surrendered Saigon to PAVN colonel Bui Tin. The surrender came over the radio as Minh ordered South Vietnamese forces to lay down their weapons. Columns of South Vietnamese troops came out of defensive positions and surrendered. Saigon fell on April 30, 1975. As for the Americans, many stayed in South Vietnam but by May 1, 1975 most Americans had fled, leaving the city of Saigon forever." Aftermath in Indochina following the Conflict: "Fear of persecution caused many highly skilled and educated South Vietnamese connected with the former regime to flee the country during the fall of Saigon and the years following, severely depleting human capital in Vietnam. The new government promptly sent people connected to the South Vietnam regime to concentration camps for "re-education", often for years at a time. Others were sent to so-called "new economic zones" to develop the undeveloped land. Furthermore, the victorious Communist government implemented land reforms in the south similar to those implemented in North Vietnam earlier. However, it is as well to remember that large areas of land in South Vietnam had already been appropriated by the communists well before the end of the war