The Observatory has said it will downgrade the T8 signal at or before 5.20am on Thursday as tropical storm Nalgae moves away from Hong Kong and weakens.

The Observatory said the T3 signal would be issued as the storm was forecast to skirt the southern waters of Hong Kong as it heads towards the vicinity of the Pearl River Estuary.

At 4am, Nalgae was centred about 50 kilometres west-southwest of the Observatory, and was expected to move northwest at about 10 kilometres per hour.

Forecasters warned that gale force winds are still affecting southwestern parts of the territory, and said seas remain very rough.

The T8 signal, issued at 1.40pm on Wednesday, was the first one issued in November since 1972.

School classes, as well as most bus and ferry services, were suspended.

The government received 11 reports of fallen trees during the storm. There were no reports of landslides or flooding.

A woman injured during the typhoon is reported to have received treatment at the Accident and Emergency Department of a public hospital.