He also extended a state of calamity -- one level below a state of emergency -- in the hardest-hit areas until February 8 as the country braces for more heavy rainfall.

The measure, first imposed on Thursday, gives authorities the power to enforce safety measures and coordinate emergency responses. It was due to expire on Sunday.

"Some areas will face more serious situations, which may even require evacuation," Montenegro said at a news conference following an emergency cabinet meeting, warning that "the ground is saturated".

The national weather agency, IPMA, has placed all of mainland Portugal on alert until Monday for heavy rain and winds of up to 100 kilometres (60 miles) per hour, with rainy conditions expected throughout the week.

"Current weather predictions are very severe and could cause major damage," national civil protection commander Mario Silvestre said.

"The soil can no longer retain water, so all the rain will run off into the basin areas. It is not a question of if, but when, and how severe it will be."

Portugal's civil protection agency has sent text alerts to mobile phones across large parts of the country warning of flood risks.

Storm Kristin's hurricane-force winds struck central and northern Portugal overnight on Tuesday, causing flooding, landslides, and damage to buildings and infrastructure.

As part of the aid package, Montenegro announced a 90-day moratorium on mortgages and other loans for residents in affected areas and earmarked 400 million euros for urgent road and railway repairs.

"We are mobilising all resources across the public, social, and private sectors to ensure that everything is fully restored as quickly as possible," the prime minister said.

Some 167,000 customers remained without power on Sunday, mainly in central Portugal -- down from over one million immediately after the storm, according to power company E-Redes.

The company's president, Jose Careto, said he could not specify when power would be fully restored, warning against creating "false expectations".

A 73-year-old man died near Leiria on Sunday after carbon monoxide poisoning from a backup generator. Two other men died on Saturday in separate falls while repairing roofs damaged by the storm.

Leiria city councillor Luís Lopes, responsible for civil protection, urged residents to take care while carrying out home repairs and to keep generators "outside in ventilated areas to stay safe".