Unidentified people assaulted four Malawi Congress Party (MCP) supporters on Saturday evening in Karonga Central Constituency during the announcement of the party's political rally scheduled for Sunday.
The incident took place at Mwenilondo Trading Centre in the area.
In an interview, MCP district chairperson Emmanuel Nkhoma said the four were injured.
"Immediately after the attack, we rushed to Karonga District Hospital for treatment," he said.
One of the victims, Absalom Banda said he was in great pain following the attack.
Karonga district director of health and social services David Sibale said the four were treated as outpatients.
In a separate interview, Karonga Police State officer-in-charge Sam Nkhwazi said they are investigating the matter.
He said: "We recorded statements from the victims and we have instituted investigations.
"However, knowing how volatile Karonga Central Constituency is, we have embarked on sensitisation campaign to civic-educate people on the dangers of political violence."
The incident has ignited fear of violence resurfacing in the constituency ahead of the November 10 by-election.
However, MCP went ahead with the rally at Mwenilondo Primary School Ground on Sunday where it unveiled Leonard Mwalwanda as its candidate in the by-election.
Addressing supporters, the party's second deputy president Harry Mkandawire condemned the incident.
"In a democracy, let everyone campaign freely everywhere because at the end of the day, it is the electorates who decide who to vote for depending on facts on the ground," he said.
Mkandawire also used the political rally to urge people to register in large numbers to vote in the by-election.
The seat fell vacant two months ago following the death of Cornelius Mwalwanda (MCP).
Nicknamed Benghazi after a time-honoured battlefield in Libya, the shoreline in Karonga has become a conflict zone since 2009 when Cornelius Mwalwanda Frank Mwenifumbo had their first-ever face-off in parliamentary poll.
Mwenifumbo is contesting in the by-election on UTM Party ticket.