The logo of MobiFone seen in front of its building in Cau Giay District, Hanoi. (Photo acquired by VnExpress)

It will offer 7.5 gigabytes of data for free to subscribers using smartphones and 1,000 minutes of calls in case of feature phones. On Tuesday many subscribers complained they were unable to make phone calls, send text messages or access the Internet from around 4.30 p.m. The issue was fixed the same evening.

A spokesperson for the state-owned company told VnExpress  it was still trying to determine how many subscribers were affected by the issue. Many people have expressed indignation that the problem occurred and the fact the operator was slow in notifying them about it. They were unable to contact the operator either during the disruption. 

MobiFone is the third-largest network operator in Vietnam after Viettel and VNPT.