A 78-year-old man is in custody as Ottawa police investigate two suspected cases of arson, capping off a busy Sunday for Ottawa Fire Services.

Emergency crews were called out to four house fires on Sunday.

Two in Ottawa's south end are being investigated by the Ottawa police arson unit.

Walkley Road fire

Ottawa Fire Services say they were called out to this home on Walkley Road just after 9:08 a.m. on Sunday. The said the fire was spreading quickly. (Robyn Miller/CBC)

Around 9:08 a.m. firefighters received a call that a home on the 1200 block of Walkley Road was on fire. The caller said the home's back windows erupted.

When Ottawa Fire Services arrived they found the basement engulfed in flames. Neighbours told crews they could hear explosions.

The fire spread quickly and by 9:17 a.m. firefighters called in a second alarm dispatch to battle the flames.

Ottawa police say a man was seen leaving the area in a van.

The fire knocked out power to more than 2,800 customers in the area, but it was later restored.

Arson cases linked, police

A few hours later at 12:45 p.m. crews headed out to a home on Leitrim Road, between Hawthorne and Ramsayville roads, for another fire call.

Ottawa fire spokeswoman Danielle Cardinal described the residence as a single-family dwelling with a large detached garage and derelict vehicles on the property. 

Extreme fire conditions forced firefighters out of the structure, but they continued to fight the flames from outside.

A German shepherd named Tequila fled the home and was later found in a field, said Cardinal.

No one was injured, but emergency fires say both homes suffered substantial damage.

Police say the arson cases are linked.

A suspect was arrested in his vehicle along Highway 417 near Pinecrest Road.

Busy day began at 7:30 a.m.

Sunday was no day of rest for the city's firefighters.

Just minutes before the Walkley call came in a homeowner on Opeongo Road called 911 to report a chimney fire. It was upgraded to a two-alarm fire when the flames spread from the chimney to the home's walls. 

The day started with a call at 7:30 a.m. Neighbours had to be evacuated on Booth Street after someone reported smoke coming from a home.

There were reports of injuries in the Booth Street and Opeongo Road fires.

Investigators are still trying to figure out the causes.