Eucodorean authorities have said six people arrested in connection to the assassination of the country's presidential candidate Fernando Villavicencio are Colombian nationals and gang members.

Ecuador’s Interior Minister Juan Zapata said in a news conference on Thursday as quoted by CNN that the suspects are members of organized criminal groups, citing preliminary evidence.

He later confirmed to the American news channel that the suspects are Colombian nationals.

However, the nationality of the suspected gunman is not clear.

Ecuador's upcoming presidential election was bloodied by the assassination of the presidential candidate at a campaign rally in the capital city on Wednesday amid an escalation in drug cartel fuelled violence in the South American nation.

Fernando Villavicencio, who was campaigning against gangs, corruption and drug dealers, was shot dead in the capital Quito.

A suspect was also killed in the shootout, said Ecuador's president  Guillermo Lasso, assuring that the guilty would be punished.

"Organised crime has come a long way, but the full weight of the law will fall on them,” Lasso said as he declared a state of emergency for 60 days.