The patients were found infected with the deadly Plasmodium falciparum parasite, which spreads malaria via the bite of a female Anopheles mosquito feeding off humans.

Malaria, often fatal, typically causes intense fevers, debilitating chills, vomiting, and associated flu-like symptoms. It is commonly found in tropical and subtropical regions skirting the equator.

Dr. Tran Van Giang of the Department of Viruses, Parasites and HIV at the National Hospital for Tropical Diseases in Hanoi said six of the malaria sufferers were also diagnosed with Covid-19.

Of the six, three have since recovered from malaria, he added.

The remaining malaria infectees have been "responding well" to hospital treatment and are recovering.

Giang explained patients contracting both diseases simultaneously suffer greater organ damage than normal, complicating the treatment process.

The hospital has measures in place to treat malaria, having received scores of infected Africa returnees.

So far, 21 of the 219 citizens repatriated from Equatorial Guinea have tested positive for the novel coronavirus, opposed to the prior figure of 129.

The returnees were employed at Sendje Hydropower Plant under labor contracts signed by Duglas Alliance Ltd of the U.K. and three Vietnamese companies.

They had sought help earlier last month from Vietnamese representative agencies in Angola. The Vietnamese government then ordered a special flight to bring them home, including those infected with Covid-19.

Upon landing, all passengers and flight crew were quarantined for 14 days at the Hanoi hospital.

Over 16,000 Vietnamese have been brought home from overseas on dozens of special flights since early April, according to the Ministry of Foreign Affairs.

Vietnam has recorded 717 Covid-19 infections so far, including 381 recoveries and 327 active cases. Nine patients, mostly elderly and suffering pre-existing illnesses, have died the past week, including one Thursday morning.