Tropical cyclones have combined with heavy monsoon rains to lay waste to swathes of Asia, killing more than 1,100 people as of Monday, with the death toll expected to rise, and leaving many more homeless.

A confluence of three tropical weather systems – including a rare cyclonic storm that built up in the strait of Malacca – has fuelled intense wind and rainover the past week, devastating areas of Indonesia, Malaysia, Thailand and Vietnam with flooding and mudslides.

Parts of the Indonesian archipelago have been particularly hard hit by flooding, killing at least 604 people and leaving 464 missing. Nearly 300,000 people have been displaced and nearly 3,000 houses damaged, including 827 that were flattened or swept away.

In the Indonesian island of Sumatra, videos circulating on social media showed people scrambling across crumbling barricades, flooded roads and broken glass to get their hands on food, medicine and fuel.

Cyclones ​usually do not form close to the equator, as force​s related to the Earth’s rotation is not strong enough to swirl them into a spin. But Cyclone Senyar formed just north of the equator in the strait of Malacca last week.

Indonesia’s meteorology agency said the formation of Senyar was a “rare” event, although one that had become more frequent in the past five years.

“Indonesia’s location near the equator theoretically makes it less prone to the formation or passage of tropical cyclones,” said Dr Andri Ramdhani at Indonesia’s meteorology, climatology and geophysics agency.

Rescuers brave flood waters by holding a rope in their effort to evacuate people trapped in their houses in Padang, West Sumatra province, Indonesia. Photograph: Rezan Soleh/AFP/Getty Images

A woman cleans mud from a house in the Meureudu area of Pidie Jaya in Indonesia. Photograph: Hotli Simanjuntak/EPA

Two other storms have compounded the destruction: Typhoon Koto caused severe flash floods in the Philippines before nearing Vietnam, while Cyclone Ditwah devastated Sri Lanka.

In Sri Lanka, the death toll from floods and landslides had risen to 366 as of Monday, with 367 missing. The country’s disaster management centre said more than 1.3 million people across the country had been affected by the record rainfall.

It is the worst extreme weather to hit Sri Lanka in two decades, and officials said the extent of damage in the most badly affected central region was only just being revealed as relief workers cleared roads blocked by fallen trees and mudslides.

Thousands of police and military personnel are distributing food, clearing roads and moving trapped families to safety. Nearly 148,000 people have been displaced from their homes and are being housed in temporary shelters.

Tropical cyclones are powerful spinning storms​ that bring heavy wind and rain. ​The most powerful ones that form in the Caribbean or North American region are known as hurricanes​, while those in east Asia are often described as typhoons, and those in the Indian Ocean (such as Ditwah) are known simply as cyclones.

Monsoons are shifting seasonal wind patterns that can bring significant rain.

Human-caused climate breakdown has increased the occurrence of the most intense and destructive tropical cyclones, though the overall number every year has not changed globally. This is because warming oceans provide more energy, producing stronger storms. Extreme rainfall is more common and more intense because of human-caused climate breakdown across most of the world.

Sri Lanka’s president, Anura Kumara Dissanayake, who declared a state of emergency to deal with the disaster, vowed to build back with international support. “We are facing the largest and most challenging natural disaster in our history,” he said in an address to the country. “Certainly, we will build a better nation than what existed before.”

An aerial view shows houses partly submerged in flood waters after heavy rainfall in Kaduwela on the outskirts of Colombo on 29 November. Photograph: AFP/Getty Images

An elderly man is carried through a flooded street in Wellampitiya on the outskirts of Colombo. Photograph: Ishara S Kodikara/AFP/Getty Images

The rains have subsided across Sri Lanka but low-lying areas of the capital, Colombo, remained flooded on Sunday, sparking a huge relief operation.

Thailand’s ministry of public health said at least 170 people had died, after some of the worst flooding in a decade.

Two boys look at a car surrounded by high flood waters in Hat Yai in Thailand’s southern Songkhla province on 26 November. Photograph: Arnun Chonmahatrakool/Thai News Pix/AFP/Getty Images

Authorities have been working to deliver aid and clear the damage, and have offered compensation of up to 2m baht (£47,000) for households that have lost family members. But there has been growing public criticism of Thailand’s flood response, and two local officials have been suspended over their alleged failures.

The rains from Koto killed three people in Vietnam, authorities said, after two boats sank amid strong winds and high seas along the flood-hit central coast.

An aerial view of Xuan Dai Bay after floods swept through the area on 25 November in Dak Lak province, Vietnam. Photograph: Thanh Hue/Getty Images

Heavy rains have lashed central areas of Vietnam in recent weeks, flooding historic sites and popular holiday destinations and causing hundreds of millions of dollars in damage.

People wade through flood water in Nha Trang, Khanh Hoa province, Vietnam, on 20 November. Photograph: EPA

Vietnam’s weather bureau has forecast rains of up to 150mm (6in) on Tuesday and Wednesday in regions that have only just recovered from historic floods.

In Malaysia, two people were killed after floods left stretches of northern Perlis state underwater. There are still about 18,700 people in evacuation centres, according to the country’s national disaster management agency.

The Associated Press, Agence France-Presse and Reuters contributed to this report