Americans have unexpectedly come ashore in Canada for the second time in less than a week — but they weren't wayward partiers — they came here to save lives.

It was just after 1 a.m. Thursday when U.S. Border Patrol marine units based in Buffalo, N.Y., noticed a house on fire on the Canadian shoreline near Niagara Falls, Ont.

The border agents didn't spot any firefighters or rescue vehicles, so they manoeuvred their boats close to shore and set off their sirens and shone spotlights to alert the residents.

The agents eventually came ashore and one led a family of four, including two children, out of the burning house to a safe spot across the road.

U.S. Customs and Border Protection says a second agent led another family of four to safety from a house adjacent to the blaze while the commander of a second American patrol boat contacted the RCMP to let them know what was going on.

This friendly cross-border invasion follows an incident last Sunday when some 1,500 wayward Americans washed ashore in Sarnia, Ont.

The unexpected visitors were on inflatable rafts and boats — attending the annual Port Huron Float Down — when they drifted off course due to high winds and strong currents.

"The decisive actions made by the agents involved demonstrates their willingness to go above and beyond to ensure the safety of citizens on both sides of the border," said Matt Harvey, the acting deputy patrol agent at the Buffalo station.