At least 13 people in Bangladesh have been killed and 4.5 million affected by floods following heavy rains, the disaster management and relief ministry said Friday.

The South Asian nation of 170 million people, crisscrossed by hundreds of rivers, has seen frequent floods in recent decades and is among the countries most vulnerable to disasters and climate change, according to the Global Climate Risk Index.

A bulletin from the disaster ministry on Friday said: "4.5 million people have been affected, and 13 people have died across the country."

Nearly 190,000 others were taken to emergency relief shelters, according to the bulletin.

Altogether, 11 of the country's 64 districts were affected by the flooding, the bulletin added.

Feni, about 100 kilometres (60 miles) northwest of the main port city of Chittagong, was worst-hit.

"It's a catastrophic situation here," rescue volunteer Zahed Hossain Bhuiya, 35, told AFP in Feni. "We are trying to rescue as many people as we can."

According to Chief Administrative Officer of Ramu district, Rasedul Islam, three of those who died drowned in floodwaters in the southeastern region of Cox's Bazar, Al Jazeera reported.

Bangladesh faces widespread destruction from annual monsoon rains every year, but climate change has triggered the shifting of weather patterns and has caused an increase in the number of extreme weather events.

The army and the navy have been deployed, with speedboats and helicopters rescuing those stranded by the swollen rivers.