A clash erupted between the agitators and the police at a border point near Birgunj during the demonstration staged by the United Democratic Madhesi Front (UDMF).
According to the police, the clash erupted when the police tried to stop the leaders and cadres of UDMF from installing tents at the border point.
The police fired in the air once and lobbed teargas shells to control the situation. Eight persons, including two policemen, were inured in a clash.
The protest came after Madhesi groups decided to ratchet up their ongoing agitation against the new Constitution.
Madhesis are Indian-origin people living on the foothills of Nepal's Terai region.
More than 40 people have died in southern and western Nepal where Madhesi parties and Tharu ethnic groups have been protesting for more than a month over splitting the country into seven provinces.
Security has been tightened at the Indo-Nepal border crossings due to increasing violence, affecting the supply of the essential goods like sugar, salt, food and cooking gas cylinders.
Only four vehicles entered Nepal from Sunauli as of 2 pm today, while on a regular day 300-400 goods carriers used to enter Nepal.
