Argentinian president Cristina Kirchner and her allies have taken a beating in mid-term elections, shrinking her majority in Congress, and ending chances of a constitutional change to allow her a third term.

Voters went to the polls on Sunday to choose half of the lower House of Deputies, and a third of the Senate.

Candidates sponsored by Argentine opposition leader Sergio Massa won in the key province of Buenos Aires, according to partial results, Interior Minister Florencio Randazzo said.

Massa, the mayor of the affluent Buenos Aires town of Tigre, headed his own list of candidates for Congress and is seen as a possible, business-friendly presidential contender in 2015.

"Tomorrow, we start with a new political map," said Buenos Aires mayor Mauricio Macri, another possible presidential candidate who promises a shift toward market-friendly policies.

Other exit polls announced on television showed Kirchner's candidates losing in key provinces around the country.

Some politicians had said they wanted a constitutional amendment to allow the ailing president to run for a third term.

But the poor showing by Kirchner's branch of the Peronist party in the mid-terms dashed those hopes once and for all.

To push through the legislation, they would need two-thirds support in both houses. If the exit polls prove accurate, Kirchner would not come close to achieving that level of support for another run for the presidency.

Health issues

Kirchner was unable to campaign for her congressional candidates since an October 8 operation to remove blood that pooled on her brain after she fell and hurt her head in August.

She is expected to continue convalescing for another few weeks.

The surgery marked the latest in a series of health issues for the 60-year-old leader, including low blood pressure and a thyroid tumor that also was surgically removed.

Speaking to local television, Kirchner's son, Maximo Kirchner, declined to speculate on when his mother would return to work. "She's okay. She's in a good mood," he said.