PHILADELPHIA -- The most immediate threat to the thousands of visitors and protesters converging here for the Democratic National Convention is likely to be the extreme heat expected to extend through the four-day event.

With temperatures hovering near triple digits, Mayor Jim Kenney said Sunday that the city is taking extraordinary precautions, deploying medics to each protest march along with pallets of water and opening fire hydrant sprinklers to keep demonstrators hydrated.

"It is important to take the extreme heat seriously," Kenney said.

The heat could affect a range of security operations, Kenney and Police Commissioner Richard Ross said, including the number protesters -- now estimated to run as high as 50,000.

The heat could affect a range of security operations, Kenney and Police Commissioner Richard Ross said, including whether the high temperatures and stifling humidity discourage some of the estimated 50,000 protesters expected each day.

In addition to the medics and water supplies, city officials are establishing two medical tents and two water misting tents to tend to protesters and visitors.

"It's going to be tough with the heat," Ross said, adding that officials know of no other credible threats to the convention involving groups or individuals.

No arrests have taken place during pre-convention demonstrations downtown Sunday afternoon, and no citations were issued involving convention-protest activity, Ross said.

Kenney said officers would be using civil citations in an attempt to cut down on the the number of arrests during the convention, when appropriate, to avoid unnecessary detentions.

In response to the Bastille Day terror attack earlier this month in France, Ross said the security plan was tightened in recent days to blunt a possible assault by a large truck. More than 80 people were killed in the French coastal city of Nice when a 31-year-old Tunisian man plowed his delivery truck into a large crowd that had gathered to view fireworks along the scenic city's main promenade.

"We would be remiss if we didn't take extra precautions," Ross said.

The commissioner declined to detail those contingencies, other than to note additional barricades had been placed along strategic routes.

Philadelphia deployed a team of police officials to Cleveland to gather information about security operations during last week's Republican National Convention, where far fewer protesters than expected participated in demonstrations there.

In Cleveland, police reported just 24 arrests during the four-day Republican gathering. One botched flag burning accounted for 17 of those detentions.

"I don't know what will happen here," Ross said. "It's way too early to get into numbers."

Kenney said the early protester estimates were gathered from permit applications. The mayor said it is possible, as occurred in Cleveland, that only a fraction of those numbers materialize.

"I am cautiously optimistic that things will go well,'' Ross said.

The commissioner said security officials have learned a great deal from past major events, including last year's visit of Pope Francis, which drew 1 million people to the city.

"The pope's visit was this (event) times five or six,'' Kenney said.

He urged the people of the city to make good on its reputation as the "City of Brotherly Love."

"Let's show some love,'' Kenney said "The country is hurting, it needs some hope, it needs some energy.''