The mother of a politician from Greece's ruling New Democracy party has died of injuries sustained in one of a series of suspected arson attacks targeting party officials.

Vagia Nestora, 72, suffered extensive burns and multiple organ failure, according to the hospital where she was taken in the northern city of Thessaloniki.

She was wounded in an explosion and fire at the apartment building where her daughter, Afroditi Nestora, lives.

Three separate attacks involving petrol bombs and other improvised devices took place within minutes of each other in Thessaloniki in the early hours of Wednesday.

Prime Minister Kyriakos Mitsotakis said Vagia Nestora's death had exposed the "murderous and inhumane nature" of political violence and called for a united response to "banish terrorism to... the margins".

Earlier, he said those who had carried out such attacks under the guise of social struggle were "nothing more than criminals, they will be treated as such".

Hospital officials said Vagia Nestora had been admitted in a critical condition with burns covering about 80% of her body and she died later despite receiving intensive care treatment.

Her daughter, a party candidate, also suffered burns and smoke inhalation and remains in hospital. Afroditi Nestora's father, who has underlying health problems, and two other residents were also admitted after suffering breathing difficulties.

Police said improvised incendiary devices had been placed outside the apartment building, triggering the explosion and fire. The blast destroyed two cars, damaged several motorcycles and caused extensive damage to the building.

The two other attacks targeted the homes of Zisis Ioakeimovits, chairman of New Democracy's Thessaloniki administrative committee, and former New Democracy MP Savvas Anastasiadis. No injuries were reported in those incidents.

Reports suggested the three attacks took place at 04:18, 04:23 and and 04:35 on Wednesday. Police believe the three attacks were carried out by the same perpetrators, whom they suspect travelled by motorcycle and placed the devices in quick succession.

Greece's Counter-Terrorism Service has taken over the investigation. No group has said it was behind the attacks and no arrests have been made.

Greece's opposition leader Nikos Androulakis said those responsible for Vagia Nestora's death "must be arrested, brought to justice and punished".

"In a democratic society governed by the rule of law, there can be no tolerance for criminal acts," he added.

The country's former prime minister Alexis Tsipras also condemned the attack, saying "terrorism has no place in a democracy".