ROAD closures on the streets of Singapore to prepare for the city-state's first Grand Prix have left commuters facing long delays.

Ahead of Sunday's first Formula One night race ever, authorities on Tuesday shut or partially closed 15 roads to make way for the 5.067-kilometre circuit that snakes around the downtown Marina Bay area.

'I saw people getting down from their cabs and walking,' a local newspaper quoted one commuter, Mr K.M. Teo, 38, as saying. He said his taxi ride to work cost three times more than usual because of the longer journey.

Ms Vikash Sianha, 30, was quoted as saying she decided to get off her bus and walk when it got stuck in a traffic jam.

'It usually takes me 15 minutes, but it took me nearly an hour to get to work today,' she said.

The initial road closures will last until Thursday, before a second phase of shutdowns takes effect on Friday when practice for Sunday's event begins, the Land Transport Authority said.

The government has warned about worsening congestion on the roads in Singapore, an island nation that is one of the world's most densely populated countries.