It comes three days after another advertising agency, Dentsu, was raided by prosecutors and the Japan Fair Trade Commission.

Event production company Cerespo was searched too, after the third-largest advertising company in the country, ADK Holdings, reported it had participated in bid rigging.

Hakuhodo is being investigated on suspicion of manipulated bids related to test events at the Olympics, according to Kyodo News.

Of the 56 open bids held in 2018 for test events, 26 of them are alleged to be rigged.

Contracts totalled more than 500 million yen (£2.9 million/$3.6 million/€3.4 million) for these test events.

Approximately half of the 26 test events had one company make a bid, according to Kyodo News' source.

A total of nine companies won the rights to the 56 test events, of which six are involved in the ongoing investigations.

"We will fully comply with the investigations," said a Hakuhodo spokesperson.

It is the second-largest advertising specialist in Japan, meaning all of the top three companies in the industry have been linked to the corruption allegations.

Same Two and Fuji Creative, two event production companies, were involved in searches today too.

Hakuhodo won two bids costing 40 million yen (£240,200/$290,090/€278,680), while Tokyu Agency - who were also searched - won three for 65 million yen (£390,260/$471,279/€452,855).

Event production companies Same Two won two for 65 million yen too, with Fuji Creative winning two for 40 million yen as well.

Another Fuji Creative bid was won for 13 million yen (£78,015/$94,231/€90,519).

These allegations suggest prior arrangements were made with Tokyo 2020 members before bidding was open.

First reports of corruption came when former Tokyo 2020 Organising Committee member Haruyuki Takahashi was alleged to have taken bribes to the tune of 200 million yen (£1.2 million/$1.4 million/€1.3 million) from five companies.