Special Central Bureau of Investigation (CBI) Judge SwaranaKanta Sharma granted four days police custody "considering the nature of crime".
"Considering the nature of crime, custodial interrogation is essential to find out the source of bribe amount and also the actual beneficiary and other conspirators other than those named in FIR," the court said.
The investigating agency produced Singla, Sandeep Goyal, Dharmendra Kumar, and Vivek Kumar before the special CBI court.
In a major embarrassment to the Congress-led UPA government, the CBI on Saturday arrested railway minister Pawan Kumar Bansal's nephew Vijay Singla for allegedly taking a bribe of Rs 90 lakh to ensure the promotion of a top railway official.
Bansal, the first Congress politician to head the railway ministry in dcecades, quickly distanced himself from his nephew's arrest in Chandigarh and said he had "no knowledge or clue" about the episode.
A furious opposition sought the resignation of both Prime Minister Manmohan Singh as well as Bansal, who returned Saturday to Delhi from his constituency Chandigarh and met prime minister.
Details of the Bansal-Manmohan Singh were not known.
Singla, a multi-millionaire businessman from Chandigarh who is Bansal's sister's son, his friend Sandeep Goyal and two others were taken by the Central Bureau of Investigation to New Delhi for further questioning. The four will be produced in a court in New Delhi.
The other two, identified as Dharmendra Kumar and Vivek Kumar, allegedly carried the bribe money to Singla Friday evening. The fifth arrested person was identified as Manjunath, who acted as a conduit.
Singla was accused of allegedly accepting a bribe of Rs 90 lakh from senior railway officer Mahesh Kumar for his (Kumar's) appointment as a member of the powerful Railway Board.
Kumar, who tried to cover his face with a handkerchief when he was arrested from Mumbai Friday night, was general manager of Western Railway until he was made a Railway Board member Thursday.
The CBI arrested Kumar from Mumbai airport soon after he landed from New Delhi. He is likely to be brought to New Delhi.
In a written statement, Bansal said: "Though a close relative, he or any other relative of mine does not and cannot meddle in my official functions or influence my decisions. I have no business relations with my nephew nor any financial transactions with him."
Bansal stressed that he has "always observed the highest standards of probity in public life and looks forward to an expeditious investigation by CBI in the matter".
But the Bharatiya Janata Party (BJP) said Bansal should be sacked and prosecuted.
"We not only demand that Bansal be sacked, he should be prosecuted by CBI under 13 of Prevention of Corruption Act. If any public servant abuses his position to obtain benefits for himself or any other person, he or she is to prosecuted and convicted," BJP spokesman Ravi Shankar Prasad said here.
The BJP leader also sought the prime minister's resignation.
"The BJP is duty bound to reiterate that you please resign as the PM of India because you do not have any moral right to govern because India is increasingly getting established as the most corrupt regime under you."
The Aam Aadmi Party also asked Manmohan Singh to sack Bansal, saying the latter's claim that he was innocent was impossible to believe.
The Congress brushed aside the resignation demands.
"The opposition has a habit of asking for resignations. It has become a disease for the opposition to demand resignation of ministers," its general secretary Janardan Dwivedi told reporters.
He said the railway minister had given had made his stand clear.
In Chandigarh, the CBI teams raided Singla's palatial residence in Sector 28 through Friday night. Singla's residence is located close to the residence of the railway minister.
A CBI official said Singla had actually demanded a bribe of Rs 10 crore from the railway official but later agreed to accept Rs 2 crore.
CBI sources said the telephone calls of Singla, Kumar and others were being monitored for the last few days before the CBI decided to make the arrests.