The deadline was moved at the request of a candidate buyer, the agency said in a press release.
Binding bids have to be placed by March 12, it added.
A total of 2,325,087 shares in the company, equivalent to 100% of its capital, were put up for sale last month.
Eligible strategic investors should have had a rail freight transport licence for the last five years and a turnover of at least 100 million euro ($132.8 million) in each of the last three years. Financial investors are required to have had at least 400 million euro in assets or equity holdings under management in each of the last three financial years.
Local news daily Standart reported last week that tender papers have been purchased by six persons - local consultancy Urista Group, law firms Georgieva, Todorov and Co. and Grigorov and Partners, lawyers Valentin Ivanov and Todor Angelov and Bulgarian Railway Company (BRC), controlled by Agropolychim and Romania’s Grup Feroviar Roman.
According to Moscow-based daily Kommersant, the Russian Railways is interested in the tender.
($ = 0.7533 euro)