Layer up — it’s cold out there. The city hit its first freezing start of the season this morning, triggering a Code Blue alert across the five boroughs.

Under a Code Blue, outreach teams head out overnight to check on anyone sleeping outside or in the subway system. If you see someone who might need help, officials say you can call 311 to get them connected to a shelter.

For those staying indoors, city officials are reminding residents that heat season rules are in full effect. If the temperature outside dips below 55 degrees, your landlord must keep your apartment at least 68 degrees during the day. Overnight from 10 p.m. to 6 a.m., the temperature inside must stay at least 62 degrees, no matter how cold it gets outside.

You should also always have hot water, even in the middle of winter. If that’s not the case, the city says to reach out to your building’s super first — and if it’s not fixed quickly, file a complaint by calling 311.

City officials are also urging New Yorkers to check on neighbors, especially older adults or anyone who might have trouble getting around or turning on their heat.

For the people bracing the cold temperatures and strong wind gusts on Tuesday, it was all about layers.

"This is the first time I've been to New York during this time,” said one woman visiting from Belize. “My aunt and my grandmother told me ‘make sure you are layered’ so I came prepared."

"Making sure that I have a good sweater on,” said a Brooklyn resident. “If I know the temperature is going to get a little chillier at night."

If Tuesday’s weather was any indication of the winter ahead, many say you may catch them outside less.

"I don't like the cold,” said Rod Batts. “Even in the summer time I don't even use the air conditioning."