The new tragedy comes just days after Typhoon Mangkhut pounded the nation's north with heavy winds and rain, sparking a separate landslide that left dozens dead.

Florence slowly crawled over South and North Carolina, dumping heavy rains on already flood-swollen river basins that authorities warned could bring more death and destruction.

The centre of Florence is expected to hit North Carolina's southern coast on Friday, then drift southwest before moving inland on Saturday.

The wet weather was the first farmers in some areas had seen for more than a year, and even included hail.

Dozens of people are missing and 1.2 million are sheltering in the camps, state officials said, as water receded and a huge clean-up gathered pace.

A vast span of the Morandi bridge caved in during a heavy rainstorm on Tuesday, sending about 35 cars and several trucks plunging 45 metres onto the railway tracks below.

At least 22 people were killed and five critically injured in Tuesday's collapse of a motorway bridge running over the north-western Italian port city of Genoa.

Japanese rescue workers searched the ruins of homes Thursday looking for dozens of people still missing after deadly rains that killed more than 200 people.

The dive team, led by international experts, returned to the cave mid-morning on Monday earlier than expected.

Oman News Agency reported that the cyclone will intensify within 12 hours.

The chances of rain in the country are expected to improve on Saturday, the Qatar Met department has said, while also forecasting strong winds and high seas in some offshore areas on Friday.

Heavy rain over the last 24 hours has blocked roads and disrupted traffic in South Africa's drought-hit Cape Town, city officials said on Thursday.