"We win! We win!" Castro, Honduras's former first lady who is making her third presidential run, told cheering Liberty and Re-foundation party supporters on Sunday.

"Today the people have made justice. We have reversed authoritarianism."

Preliminary results released late on Sunday by the Electoral Council showed Castro with 53 per cent of the votes and the National Party's Nasry Asfura with 34 per cent, with 38 per cent of voting stations counted. The council said turnout was more than 68 per cent.

Honduras's long-ruling National Party announced on its Twitter account that Asfura, the major of Tegucigalpa, had won.

The competing claims of victory came just hours after the National Electoral Council reminded parties that such announcements were prohibited and violators would be fined.

The claims raised fears of street protests and violence and some businesses on Tegucigalpa's main boulevard boarded over their windows as a precaution.

The National Party's 12-year rule has been beset by graft scandals, chronic unemployment and waves of fleeing migrants.

If she wins, Castro would become Honduras's first female president and her victory would mark the left's return to power for the first time since her husband, former president Manuel Zelaya, was deposed in a 2009 coup.

She has gained favour from voters for her efforts to consolidate opposition to outgoing President Juan Orlando Hernandez, who has denied accusations of having ties to powerful gangs, among other corruption scandals.

Australian Associated Press