Security guards cordoned off the building in the Shiodome district of Japanese capital Tokyo in response to the threat.

Japanese news agency Kyodo reports that the threat claimed "a bad company that disturbs the world will be disciplined", saying a bomb would detonate tomorrow morning.

Due to restrictions on overcrowding in place to prevent the spread of coronavirus, the office was operating at roughly 20 per cent capacity.

Dentsu was appointed as the exclusive Olympic and Paralympic marketing agency in Japan a year after Tokyo was awarded the Games in 2013.

With the Games now postponed until 2021 and a global economic downturn underway, Dentsu said last month that it anticipates "a material decline in revenues" this year because of the coronavirus pandemic.

The second quarter from April to June "is expected to be the weakest quarter of the year", the company said, withdrawing a previous forecast of net profits of JPY46.7 billion (£359 million/$440 million/€399 million) in 2020.

Reduced working hours and temporary salary reductions are among the cost-cutting measures Dentsu has implemented in response to the pandemic.

The company recently obtained a contract worth JPY76.7 billion (£553 million/$700 million/€620 million) to provide administrative services for a Government scheme to assist firms impacted by the COVID-19 crisis.

Opposition parties were critical of how Dentsu attained the contract and have suggested it is an inefficient use of taxpayers' money, although Dentsu insists it has followed Government rules.

The agency has previously been forced to disassociate itself from allegations it was involved in corruption cases due to its close links with disgraced former International Association of Athletics Federations official Lamine Diack.