The explosion occurred last Thursday when people were trying to syphon off petrol from the tanker after it was abandoned by its driver, officials said.
"We can inform to you that 73 of our citizens have so far lost their lives as a result of the accident," Minister of State Administration Carmelita Namashulua told a press conference.
The tanker loaded with 30,000 litres of petrol exploded in Tete province, a remote western region near the border with Malawi, killing 43 people on the spot, with over 100 badly burnt including children.
Some of the victims being treated at Tete Provincial Hospital were children, in a disaster that President Filipe Nyusi called a "tragedy".
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The government yesterday declared three days of national mourning and has set up a commission to investigate the cause of the blast.
The driver is said to have disappeared.
Namashulua said some villagers continued to drain petrol from the truck after the blaze was put out, using plastic jars and hoses.
The government in Mozambique, one of the world's poorest countries, recently increased the price of fuel after the value of the local currency -- the metical -- fell sharply.