Heavy rain from a weather system has caused widespread flooding across eastern Canada, with a state of emergency being declared in Montreal.

The weather system is the same one which brought severe storms to parts of the southern US and flooding to the eastern seaboard. Flooding was from northern Virginia to New York and New Jersey.

That same weather system, containing a mass of moisture-laden air originating in the Gulf of Mexico, has now moved across eastern Canada.

There had been concerns about the potential for flooding across the region, following one of the wettest Aprils in many years, plus the effect of snowmelt. The level of Lake Ontario was already at a 20 year high.

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Now Montreal, which lies 200 kilometres to the northeast of Lake Ontario, has been inundated following a deluge of at least 80mm of rain between Friday and Sunday.

Flooding is now a concern all the way from Toronto and Lake Ontario downstream along the St Lawrence River.

The Ministry of Public Safety said waters were expected to crest sometime Monday in Quebec province.

Rising floodwaters prompted Montreal Mayor Denis Coderre to declare a state of emergency on Sunday afternoon. This was expected to remain in force for 48 hours.

Officials in Toronto are also monitoring the situation with the city's mayor, John Tory saying that homes on Ward's Island were, "potentially in jeopardy" if more rain falls.

New evacuations were carried out in Pierrefonds on the northwestern shore of the Island of Montreal as water levels rose rapidly following the breaching of three dykes.

The heaviest rainfall seems to have been in New Brunswick, where a weather station northeast of Saint John recorded 155mm of rain between late Friday and the early hours of Sunday.

At least 1,900 homes have been flooded in Quebec alone, and more than 1,000 residents have been affected.

Around 1,200 Canadian Forces personnel have been drafted in to help with relief efforts.

Harjit Sajjan, defence minister, was quoted as saying: "Our troops are responding quickly and professionally and are already beginning to deliver critical support to Canadians affected by the flooding."

The rainfall situation is improving across the region, with the heaviest of the rain confined to the northern shoreline of the St Lawrence River and the Ile d'Anticosti.

On the other side of the country, days of heavy rain in British Columbia have caused flooding and a landslide, which is believed to have claimed two lives. Here, too, the worst is thought to be over.