The mayor of the City of Clarence-Rockland just east of Ottawa has declared a state of emergency Thursday as rain expected to arrive overnight "will create havoc," he said.

Clarence-Rockland Mayor Guy Desjardins declared the state of emergency at 5 p.m. Thursday once the city got the news of more rain coming.

"They're expecting 25, maybe as much as 70 millimetres of rain, bringing up the [water levels] by 25 to 35 centimetres, and that will really create havoc in our town," he told CBC Radio's All in a Day.

Dozens of volunteers were on hand Thursday to fill sandbags for friends, neighbours and even strangers as the Ottawa River is lapping right up to waterfront homes.

The arena in Clarence Creek has been opened to accommodate evacuees. Another meeting is planned for 8 p.m. to provide residents with more details then.

Clarence-Rockland mayor Guy Desjardins says he expects rain arriving this weekend to bring 'havoc' to the homes along the Ottawa River. (CBC)

By declaring the state of emergency, the city can get help from the provincial and federal governments and call for a mandatory evacuation, though Desjardins admits they can't force people from their homes.

"We don't have the power to throw the people out, we're just doing this, they're advised that we have a mandatory evacuation, and that's why we've opened the shelter for the people," he said.

When asked if he had ever seen water levels this high before, Desjardins said "never."

"I've been in Rockland for 40-some years, I was raised in Orleans, and I've never seen this. And especially with more coming, that's the worrisome part. What levels will it go [to] then?"