BEIJING (CNN) -- The "heaviest rain in six decades" in the Chinese capital of Beijing has left at least 37 people dead, the state news agency Xinhua reported Sunday.

The torrential downpour lasted 10 hours, with gusty winds in some areas and a tornado in one suburb, according to local media.

During the storm, traffic was paralyzed for hours, with drivers and pedestrians stranded throughout the city. Many streets were flooded with water levels sometimes as deep as 13 feet (4 meters).

Thousands of emergency responders were deployed and divers had to be brought in to search for anyone trapped.

Officials said almost 2 million people were affected by the rainstorm and the economic losses have exceeded $1.5 billion.

Drowning is the leading cause of death, taking 25 lives, Xinhua reported. But six people were killed by collapsing houses, five were electrocuted, and one was hit by lightning, the agency reported, citing the municipal government.

The average rainfall Saturday was 6.7 inches, but one suburban district recorded 18 inches, Xinhua said.

Authorities have identified 22 bodies so far, the agency reported.

At the Beijing International Airport, more than 500 flights were canceled Saturday. At one point, some 80,000 passengers were stranded in the airport terminals.

Even as operations slowly returned to normal, there were reports of passengers still stranded late Sunday.

Local television broadcast heroic stories of search and rescue efforts and people helping each other, but online, people were critical.

Many complained that authorities seemed ill-prepared despite heavy rain having been forecast days in advance. Critics said there was no emergency broadcast system deployed, no government shelters and no special hotlines.

They also complained of a fragile, ill-prepared infrastructure, pointing out the sewer system was overwhelmed by the rains.

Xinhua reported the flooding submerged some power supply facilities and led to blackouts in parts of the city.