Gloucestershire issued with three severe flood warnings
Three severe flood warnings, which indicate a possible danger to life, are in place in Gloucestershire.
Three "large" Severn Bores - when the tide from the Severn Estuary is forced into narrower channels upstream - have been predicted over the next 24 hours.
Gloucestershire Police have warned people planning to watch the bores to "avoid the area completely".
The areas affected include the Severn estuary, River Severn and tidal Severn.
Rest centres in Stroud, Tewkesbury, Gloucester and the Forest of Dean are all on standby and councils are working with vulnerable people in affected areas.
'Situation changing hourly'
On the Somerset coast, nine flood warnings are in place and residents are being warned of possible tidal surges.
In Bristol, an emergency flood barrier is being deployed for the first time.
High tide on the River Severn in Gloucestershire is expected between 08:00-10:00 GMT.
And with the already-swollen river the situation was changing hourly, the Environment Agency said.
It has issued three severe flood warnings for Westbury, Broadoak and Newnham on the Severn estuary, on the tidal Severn from Elmore to Rodley and the River Severn at Minsterworth and Quedgeley.
"Our advice to people living in areas at risk of flooding is to move important documents, personal items and valuables upstairs or to high shelves," said the agency's Dave Throup.
Three large bores have been predicted to occur between 08:00-10:00 GMT and 20:30-22:30 GMT and on Saturday between 08:30-10:30 GMT.
But Simon McMillan, from Gloucestershire Fire and Rescue Service, has advised people planning to watch the Severn Bore to "avoid the area completely".
"The situation could change very fast and there is a real possibility you may get caught out," he said.
'Avoid sea fronts'
In Somerset, with a spring high tide expected to peak at around 07:45 GMT, coastal communities are also being urged to brace themselves for potential flooding.
Porlock Weir, Minehead, Dunster Beach, Blue Anchor, Stolford, Steart and Burnham-on-Sea are all likely to be hit.
Paula Hewitt, from Somerset County Council, said: "The precise impact is hard to say, but we are being told that we could be badly affected.
"We are doing what we can, but in weather like this it's important that people take common sense precautions - avoid sea front areas, don't drive into floodwaters and check on vulnerable neighbours."
The A361 at Burrowbridge in the county remains closed in both directions.
In Bristol, people living near the River Avon in Shirehampton, Bathurst Basin, St Phillips Marsh and St George are also being urged to prepare for possible flooding in the hours before and after peak tide levels.
Due to the "severity of the possible risk", the city council is installing an "emergency flood barrier" for the first time across Avon Crescent.