Builders are ripping out and repairing construction errors to part of the marathon route for August's Olympic Games, only months after the same stretch was said to be ready, officials said on Thursday.

The men's and women's marathons were meant to be one of the highlights of the Games, following the original route taken by a Greek messenger who ran from Marathon to Athens in 490 BC to declare victory over the Persians.

But work on widening the original 42-kilometre road to make it fit for the event was delayed after one of the contractors ran into financial difficulties and was taken off the project early this year.

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The mayor of Pallini said the stretch in question is a section of the marathon route that goes through the middle of town.

"The project was originally delivered as ready in December, but the new company that took over in March told us there were problems with bad construction, so they have to rip it out and re-do it," Pallini mayor Thodoros Gotsopoulos told Reuters.

"We have been through a lot with this project, it took the previous company around two years to build a stretch of around 2.5 km, and okay, they did install new sewage pipes and cables, but still that can't justify the two years," he added.

A spokesman for the Public Works Ministry said that stretch of the route had indeed sunk in parts as the previous contractor had used shortcuts in the construction process.

"When we gave the project to the new company, we knew in advance that some rebuilding would be needed," the spokesman said. "But we are fully within our time limits, by the end of June or the middle of July, the entire road will be ready."

Gotsopoulos said the new company had pledged the repairs would be done by the end of May. The government has already cut back landscaping at the starting point of the marathon in a bid to make up tight deadlines before the August 13-29 Games.