A major incident has been declared over what police have called a sinkhole at a canal in Shropshire, leaving boats either stricken in a gaping cavity or teetering on the edge of a drop.

Pictures appear to show that the structural integrity of a stretch of waterway in Whitchurch has completely given way, raising flooding fears.

Two narrowboats at the scene were said to have sunk into the hole shortly after 04:00 GMT, with another two at the edge. Water there looks to have drained away completely.

Shropshire Fire and Rescue Service (SFRS) said it was responding to a landslip and confirmed a canal was affected.

Scott Hurford, area manager at SFRS, which sent 50 firefighters, said crews received reports at about 04:20 GMT that a canal bank had collapsed and there were large volumes of water in surrounding fields.

According to West Mercia Police, there are no reports of casualties at the scene, in an area of Whitchurch called Chemistry.

The force asked people to avoid the area and seek alternate routes.

The Canal and River Trust described the incident as a breach on the canal, and said its priority was the safety of boaters and those in the immediate area.

"We are carrying out initial investigations into the possible cause of the breach and will provide more details in due course," it said.

"We will also seek to return water levels either side of the breach as soon as possible and are providing support to the boaters affected and those in the immediate area either side of the breach."

Mr Hurford told BBC Shropshire: "The information we've had back is that the canal bank failed and that's what put the emergency call in.

"The water from the canal has leaked out of the canal into the surrounding fields… There are up to 15 people who had to be moved out of the way to safety, and there's a number of canal boats that have been affected, some of those have gone into the field and some are at the bottom of the canal."

He added: "Our job is the response phase, so we're there to save life, protect property and the environment, but we will support in the recovery phase."

Andy Hall, a councillor in Whitchurch, said: "We've got two boats at the bottom of the sink hole that have fallen down, and we've got two boats that are teetering on the edge that could go in at any time," he told the BBC.

"Obviously [the fire service is] going to make those safe."

He added: "[People] thought that there was an earthquake.

"To the right, we've got the field which has taken probably about a million gallons of water out of the canal."

He said the fire service had put in a flood gate to stop the flow of more from the compromised waterway.

"The most important thing is that the canal itself has been secured by fire and rescue," he said. "Their biggest worry was that the canal was going to burst even more and flood residents in the town."

He said that no one was on board "the two boats that went down", adding that people on the boats "teetering over the edge" had been helped to safety by fire crews.

He said that contrary to speculation on social media, there had been no bridge collapse.

Lorraine Barlow, who lives on a boat called The Singing Kettle and was moored near the site, said: "About 04:20 this morning I could feel that there was something amiss, there seemed to be a current coming from underneath the boat, and bubbling, it sounded really unusual.

"Then I was tilting to the middle of the canal, I could feel the ropes were getting tight."

She said she left the boat and could see the fire service as well as search and rescue teams.

"There was no water on the canal," she said.

"I was worried about the ropes and about my canal boat hanging there.

"It's an awful thing, I was worried about the other people."