A fumaça está entrando em casa.

Because fumaça is a feminine singular noun, and Portuguese normally uses a definite article more often than English does.

So:

• a fumaça = the smoke

In English, we might say just Smoke is coming into the house, but in Portuguese, A fumaça... sounds very natural.

Está entrando is the Brazilian Portuguese way to say that something is in the process of happening right now.

• está entrando = is coming in / is entering
• entra = enters / comes in or sometimes is coming in, depending on context

So:

• A fumaça está entrando em casa. = The smoke is coming into the house right now.

This is similar to the English present continuous.

Entrando is the gerund of entrar.

• entrar = to enter / to come in
• entrando = entering / coming in

In Brazilian Portuguese, the structure:

• estar + gerund

is very common for ongoing actions:

• está entrando = is entering
• está chovendo = is raining
• estou falando = I am speaking

Because Portuguese often expresses ongoing action with:

• estar + gerund

So even though the English translation may use come in, Portuguese uses the verb entrar very naturally here.

Literally, A fumaça está entrando em casa is something like:

• The smoke is entering into the house/home

But in natural English, The smoke is coming into the house is usually better.

This is a very common learner question.

Em casa is a fixed, very common expression meaning:

• at home
• home
• sometimes into the home/house, depending on context

In this sentence, entrando em casa means the smoke is coming into the home/house.

Compare:

• Estou em casa. = I am at home.
• A fumaça está entrando em casa. = The smoke is coming into the house/home.

If you say na casa, that usually sounds more like in the house or into the house, referring to a specific building a little more explicitly:

• A fumaça está entrando na casa.

That is also possible, but em casa sounds very natural if the idea is into the home.

A useful way to think about it is:

• em casa = at home / home / into the home
• na casa = in the house / into the house, often more concrete or specific

Examples:

• Estou em casa. = I’m at home.
• Tem muita gente na casa. = There are many people in the house.
• A fumaça está entrando em casa. = The smoke is coming into the house/home.
• A fumaça está entrando na casa pela janela. = The smoke is entering the house through the window.

In many situations, both can be possible, but the nuance changes slightly.

Because estar is used for states, conditions, and ongoing situations, while ser is used for more essential characteristics, identity, origin, and so on.

Here, está entrando describes an action happening right now, so it must be estar:

• está entrando = is entering

You cannot say:

• A fumaça é entrando... ❌

That is not grammatical Portuguese.

Yes, but the meaning changes a bit.

• A fumaça está entrando em casa. = The smoke is coming into the house right now.
• A fumaça entra em casa. = The smoke comes into the house / smoke enters the house.

The second version can sound more general, habitual, or less focused on the action in progress.

So if you are describing an immediate situation, está entrando is the better choice.

Fumaça is normally used as an uncountable noun, much like smoke in English.

So:

• a fumaça = the smoke

You usually would not say as fumaças unless you were talking about different kinds or sources of smoke in a special context. In ordinary speech, singular is the normal form.

In Brazilian Portuguese, fumaça is pronounced approximately like:

• foo-MAH-suh

More closely:

• fu = like foo
• ma = stressed syllable
• ça = sounds like sa

Important detail:

• ç always has an s sound, never a k sound.

So fumaça sounds like foo-MAH-sa.

The acute accent in fumaça shows the stressed syllable:

• fu-MA-ça

Without the accent, the stress pattern would be less clear and the spelling would not be correct.

So the accent helps tell you where the voice should naturally emphasize the word.

Yes, but the original order is the most neutral and natural:

• A fumaça está entrando em casa.

You might also hear:

• Está entrando fumaça em casa.

This can sound more like Smoke is coming into the house, with focus on the event or on the fact that smoke is entering.

But for learners, the standard subject-first order is the safest choice:

• A fumaça está entrando em casa.