つつある

Indicates that a change or process is currently underway and gradually progressing toward completion: "is in the process of ~ing," "is gradually ~ing." It is typically used with verbs expressing change.

A written, somewhat formal expression common in news reports, essays, and analyses of social, economic, or natural trends. It pairs naturally with verbs of change such as 増える, 減る, 変わる, or 回復する, and emphasizes that the process is still unfolding. Compared with ている, it highlights gradual progress toward an endpoint rather than an ongoing action or resulting state.

• ているN5「ている」attaches to the て-form and is stylistically neutral, covering ongoing action, resulting states, and habits, while 「つつある」attaches to the verb stem (the ます-form minus ます), leans written/formal, and describes only a change still in progress. With change verbs, 「ている」often expresses a result: 「沈んでいる」means something has already sunk.
• ていくN4「ていく」attaches to the て-form and is stylistically neutral; for change it looks ahead to continued development from now into the future, whereas 「つつある」stresses being in the middle of the change right now. 「ていく」can also express moving away from the speaker in space, which 「つつある」cannot.
• 一方だN3「一方だ」attaches to the dictionary form (e.g., 「減る一方だ」) and is stylistically neutral; it stresses a change heading in one direction with no sign of stopping or improving, often a bad trend with a tone of concern. 「つつある」simply states objectively that a change is under way but not yet complete.
• つつN2「つつ」attaches to the same verb stem as 「つつある」 and is likewise written-style, but it links two clauses to mean 'while...' or 'although...' (often as 「つつも」); it does not express the progress of a change and is not interchangeable with 「つつある」.
• てくるN4Only in its 'change' sense is 「てくる」close to 「つつある」: it attaches to the て-form, is stylistically neutral, and describes a change progressing and coming into view up to a reference point (usually the moment of speaking, but it can also refer to the future); it is also common for small everyday matters. 「てくる」has other senses as well, such as 'go and come back' or 'come toward (the speaker)'.
• ようになるN4「ようになる」attaches to the dictionary form, potential form, or ない-form, and is often used as 「ようになった」to express that a change in ability or habit has become an established new state; it is stylistically neutral. 「つつある」stresses that the change is still in progress and incomplete, and leans written/formal.

Unlike ている, which can describe an ongoing action or a resulting state (沈んでいる can mean "has sunk"), つつある stresses that a change is still underway; ていく and てくる add a sense of direction in time, 一方だ stresses an unstoppable one-way (often negative) trend, and ようになる marks that a change has been reached. つつ on its own is a different pattern meaning "while" or "although."