The euro hit an 11-year low versus the US dollar on Monday as Greece's anti-austerity Syriza party swept to victory in a snap election, putting Athens on a collision course with international lenders.

The single currency dropped to $US1.1098, a level not seen since September 2003, as official projections showed Syriza was set to win 149 seats in the 300-seat parliament, taking 36.3 per cent of the vote.

Supporters of opposition leader and head of radical leftist Syriza party Alexis Tsipras cheer at his campaign headquarters in Athens. Credit:Reuters

The euro fell to as low as ¥130.16, its lowest level in more than 11 years. The euro also fell against sterling, hitting a seven-year low of 74.06 pence.

In the near term, traders are looking to whether Syriza will secure an outright majority, which would raise the risk of a standoff with Greece's European lenders over austerity measures as well as the stance of Syriza leader Alexis Tsipras.