The observatory on Friday said it would consider the need to issue Hong Kong’s first T10 signal since typhoon Mangkhut in 2018, as the powerful ‘eyewall’ of Super Typhoon Saola passes through the territory.

Forecasters expect the centre of the storm – still packing sustained winds of around 210 kilometres per hour – to pass just 40 kilometres south of the Hong Kong Observatory in Tsim Sha Tsui at around midnight.

As of 6.45pm, the storm was centred around 70 kilometres east-southeast of the city, and was maintaining its steady progress towards the Pearl River Estuary.

But forecasters say the eyewall of the storm – a literal wall of wind surrounding its centre – was just 30 kilometres to the east of the observatory.

“It is expected that the eyewall of Saola will move across Hong Kong in the next few hours,” the observatory said. “Winds will strengthen significantly. The observatory will assess the need for issuing the Hurricane Signal, No 10, depending on the local wind changes.”

Gale force winds were already affecting the territory, with occasional storm force winds offshore and hurricane force winds on parts of the high ground. Gusts of wind in excess of 100 kilometres per hour have already been recorded on Lamma Island, Peng Chau, Waglan island, Tate's Cairn and Cheung Chau.

And the wind direction will be changing as the storm gets closer. As the storm gets closer, northerly winds will change gradually to east to southeasterlies, meaning areas which were previously sheltered may become exposed.

Authorities are also warning of a major storm surge that is expected to lead to record-high water levels in the eastern part of the territory. The observatory says the water level at Tolo Harbour could reach four metres higher than the normal tide level at 9pm on Friday – which would be the highest ever recorded.

Other areas that are expected to face major storm surges are Sha Tin, Tai Po, Sha Tau Kok and Sai Kung, where the observatory says there will be serious flooding, with the flood depth in some areas possibly exceeding one meter.

Water levels will also rise tomorrow morning from around 6am, when the maximum water level at Victoria Harbour will be some 3 metres above chart datum.

So far, authorities have confirmed seven cases of flooding in Hong Kong, along with 29 reports of trees toppled in the storm. Three people who were injured during the typhoon period have sought help at public hospitals as of 5.40pm and more than 330 people are taking refuge at temporary shelters across the territory.