Eighty-four patients were registered in Hai Duong, 13 in northern Quang Ninh province, one in northern Hai Phong city, one in northern Bac Giang province, and one in Hanoi.
This is the largest daily increase in local coronavirus infections recorded since the pathogen first appeared in Vietnam on January 23, 2020.
The Health Ministry on Thursday confirmed seven imported cases, all of which had been quarantined upon arrival by plane from abroad.
Health officials have urged rapid contact tracing to quell the new wave, while warning of far worse scenarios.
But they are still not sure about the primary source of the new local infections, although at least 82 of the locally infected patients in Hai Duong and Quang Ninh have already been linked to two cases - patients No. 1,552 and 1,553.
Patient No. 1,552 is a 34-year-old Vietnamese woman who works for Vietnam Poyun Electronics Co. Ltd. in Hai Duong, the Ministry of Health said in a report.
She had been in contact with a woman who had left Vietnam for Japan on January 17. This woman had tested negative for the virus on January 14 and 15 before leaving Vietnam.
The woman tested positive again Tuesday in Japan for the new, 70 percent transmissible variant that has recently been rampant in the United Kingdom.
Patient 1,552 was diagnosed with COVID-19 on Wednesday evening.
Patient #1,553 is a 31-year-old Vietnamese security guard at Van Don International Airport in Quang Ninh.
He had a fever, dry cough and sore throat, so he went to the hospital for examination.
The man was tested for the novel coronavirus at the Quang Ninh Center for Disease Control on Wednesday night and the result was positive.
Vietnam has documented 1,658 coronavirus patients as of Thursday evening, with 1,430 recoveries and 35 virus-related deaths, according to a Tuoi Tre News listing.
The country had not detected local transmission for nearly two months before the new clusters were uncovered.