The Indian engineers were working at a power plant in the Baghlan province in north Afghanistan, according to local media reports.
The External Affairs Ministry said in New Delhi it is in touch with authorities in Afghanistan and is ascertaining the details of the incident.
A spokesman for the provincial governor said the blast happened while some people were busy with prayers while others had gathered to get their voter registration cards for the elections.
For now, nobody has officially claimed responsibility.
An Afghan official says that seven Indian citizens and their Afghan driver have been kidnapped in the northern Baghlan province.
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The employees were abducted while they were travelling to the area where the company owns an electricity sub-station contract, the report said.
Habib Shah Ansari, the provincial head of public health, provided the first precise toll from the attack, which was earlier confirmed by other officials.
And a auto bomb killed two people and wounded another three in the eastern Paktia province in an attack claimed by the Taliban. But the Taliban, and the local cell of the Islamic state oppose democratic elections in the country.
A blast at a voter registration centre in Afghanistan's restive east on Sunday killed or wounded at least 30 people, officials said, capping a bloody week in the war-torn country. Neither had an exact figure for casualties.
The Taliban and it is have found a constant tide of attacks since the onset of year, murdering scores of civilians from the capital, Kabul, and also elsewhere.