More than 75,000 boats were recalled as fishermen were ordered back into port and tourist activities were cancelled in Zhejiang, Xinhua said.
Schools, airports and motorways in some areas were also closed.
Early on Sunday, China's coastguard rescued 27 people from a Hong Kong freighter that suffered mechanical failure after it was hit by Krosa off the port of Wenzhou in Zhejiang, Xinhua said.
Authorities warned of possible mudslides in Fujian, which was hit by torrential rains ahead of Krosa's arrival.
Holidays for flood-control workers were cancelled in Shanghai, where the Special Olympics and the Chinese Grand Prix were under way, and plans to drain competition sites were being drafted.
Krosa killed five people on Taiwan as it knocked out power to 2.2 million homes and businesses and drenched the island, according to Taiwan's disaster relief centre.
A landslide killed two people in a mountainous area of the capital, Taipei, while isolated accidents caused by high winds killed another two. A traffic accident caused the fifth casualty, Taiwan's National Fire Agency reported.
The storm led to the cancellation on Sunday of 378 flights and the government continued to advise people against going to work or school.
Tropical Storm Risk, a British typhoon-tracking organisation, said Krosa was expected to head northeast toward Fukuoka in Japan.
Meanwhile, the toll from Typhoon Lekima, which battered Vietnam's central coast earlier this week, has risen to 55.
Another 16 people remain missing.
Thanh Hoa and Nghe An provinces were hit hardest by torrential rains, with strong winds blowing off roofs and floods submerging entire villages.
Nguyen Xuan Hanh, an Nghe An provincial official, said: "We have not seen flooding like this in 20 years. It was so fast and so out of the blue."
On Saturday, helicopters dropped food to stranded villagers while rescue workers waded through chest-high water to assist people to safety.
The government said preliminary damages from the typhoon, the fifth of 2007, stood at $41m after the storm and floods destroyed about 100,000 homes, mainly in central provinces.