In an incident similar to the 2001 Tampa affair, where Australia refused entry to Afghan asylum seekers, Singapore said it had blocked the ship because ''those aboard do not appear to be persons eligible to enter Singapore''.
The asylum seekers are believed to have been in the water for 30 hours before the ship Nosco Victory rescued them on December 5, meaning they would have been in a distressed state.
They are believed to be still aboard the ship anchored off Singapore. Their condition is unknown.

Singapore authorities said the Nosco Victory's captain ignored advice by Indian rescue authorities to take the asylum seekers to the ''nearest port of safety'', which probably would have been a Bangladeshi port.
The ship was due to dock in Singapore on Sunday.
''As information provided by the vessel's master concerning the rescued persons is sketchy and there is no other official documentation to assist at this point, they do not appear to be persons eligible to enter Singapore,'' the spokesperson said.
''Under these circumstances, MV Nosco Victory was denied entry to the Port of Singapore.''
The ship's agent could not be reached for comment.

The asylum seekers are believed to Rohingyas, a Muslim minority who were fleeing western Burma, where ethnic violence erupted in June.
They were plucked from the sea after the overcrowded Bangladesh-flagged ship Nayou sank at about midday on December 4. Up to 160 other Rohingya aboard the ship are believed to have drowned. The Nayou was en route to Muslim-majority Malaysia, where there is a large Rohingya population.

The sinking is one of at least four in the area since October that has resulted in drowning of several hundred Rohingya - stateless people described by the United Nations as among the world's most persecuted groups.
More than 4000 Rohingya have attempted the perilous journey to Malaysia in the past eight weeks as the UN describes the situation in Rohingya camps in Burma's western Rahkine state as ''dire'', with widespread starvation.
The United Nations High Commissioner for Refugees last month called on regional countries to keep their borders open to people seeking asylum and international protection from Burma.

The Maritime and Port Authority of Singapore spokesperson said the advice given to the captain of the Nosco Victory by Indian rescue authorities was made in consultation with the authority ''taking into consideration the safety and security of the ship''.