Typhoon Yagi, Asia's most powerful storm this year, left dozens dead in northern Vietnam and widespread damage as it churned westwards, preliminary government estimates showed on Monday, while the weather agency warned of more floods and landslides.

Thirty-five people have died and 24 are missing, mostly because of landslides and floods triggered by the typhoon, Vietnam's disaster management agency said.

The typhoon made landfall on Saturday on Vietnam's northeastern coast, home to large manufacturing operations of domestic and foreign companies, and was downgraded to a tropical depression on Sunday by the meteorological agency.

It cut power to millions of households and companies, flooded highways, disrupted telecommunications networks, downed a medium-sized bridge and thousands of trees and brought to a halt economic activity in many industrial hubs.

Managers and workers at industrial parks and factories in Haiphong, a coastal city of two million, said on Monday they had no electricity and were trying to salvage equipment from rain in plants whose metal sheets roofing had been blown away.

"Everyone is scrambling to make sites safe and stocks dry," said Bruno Jaspaert, head of DEEP C industrial zones, which host plants from more than 150 investors in Haiphong and the neighbouring province of Quang Ninh.

Walls of a factory in Haiphong of South Korea's LG Electronics (066570.KS), opens new tab collapsed, according to pictures and a Reuters witness.

LG Electronics, a major maker of appliance and consumer electronics, said there were no casualties among its employees and acknowledged damages at its production site noting a warehouse with refrigerators and washing machines had been flooded.

"Lots of damages," said Hong Sun, the chairman of the South Korean business association in Vietnam when asked about the typhoon's impact on Korean factories in coastal areas.

A manager of leased factories confirmed widespread damages to roofs and prolonged power cuts in northern provinces.

A bridge in the province of Phu Tho collapsed on Monday, authorities said.

"This is normally a busy bridge, a key bridge in the province," a senior official of the province's transport department said, adding there was no report available yet on casualties.

The weather agency warned of more floods and landslides, noting that rainfall ranged between 208 millimetres and 433 millimetres (8.2 inches to 17.1 inches) in several parts of the northern region over the past 24 hours.

State-run power provider EVN said that more than 5.7 million customers lost power during the weekend as dozens of power lines were broken, but electricity was restored on Monday to nearly 75% of those affected.