The Grey District Council are urging vigilance in the region as more severe weather is expected to hit this afternoon after 75mm of rainfall caused surface flooding this morning.
A welfare centre has been set up at the Westland Recreation Centre on High Street, and residents are being urged to head there if their property is at risk of flooding.
"What we've got is a a situation where we've just called a Civil Defence meeting - it's that bad," said Greymouth Mayor Tony Kokshoorn in an update.
He said the town has been closed off in and around the Ashley Motor Inn, where a creek that periodically floods is going through houses.
There is also a lot of flooding around the Sawyers Creek, which the council are currently monitoring.
Several places around the town have had to be evacuated including Barnardos on Alexander Street.
Motorists are also being advised to avoid driving through town due to the backwash from cars.
"Luckily in the last hour the rain has stopped and a lot of that floodwater has resided," said Mayor Kokshoorn.
But the council are on alert this afternoon as more rain is forecast and high tide is expected later today.
"This event is one we're working through step by step," said Mayor Kokshoorn.
"A lot of surface water has gone but we're watching it hour by hour."
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