Thessaloniki - Greek farmers protesting against pension reforms heightened highway and border protests around the country on Saturday, piling pressure on the leftist government of Prime Minister Alexis Tsipras.

Farmers in Thessaly began a one-day blockade of the main highway between Athens and Thessaloniki despite compromise efforts by the government.

The mobilisation which began in mid-January has created tractor blockades at dozens of highway locations and key border crossings to Bulgaria and Turkey, which the farmers intermittently open for a few hours each day.

"What we are doing is tiresome but we are not stopping. We will take it to the end and stay as long as it takes," local protest organiser Stergios Litos told state agency ANA.

The farmers on Saturday briefly opened the main border crossing into Bulgaria to allow some 200 freight trucks to enter Greece.

Tsipras' government has announced plans to lower the maximum pension to 2,300 euros ($2,500) from 2,700 euros currently, and introduce a new minimum guaranteed basic pension of 384 euros.

The reform is part of the country's cost-cutting efforts under its EU bailout.

The government also wants to merge insurance funds and increase social security contributions by both employers and staff.

Farmers are also angry as the government plans to scrap benefits such as income tax breaks and cheaper fuel.

The income tax rate for farmers is also to progressively double to 26 percent. The government has invited farmer leaders to talks on Tuesday.